NORME
INTERNATIONALE
INTERNATIONAL
STANDARD
CEI
IEC
62305-3
Première édition
First edition
2006-01
Protection contre la foudre –
Partie 3:
Dommages physiques sur les structures
et risques humains
Protection against lightning –
Part 3:
Physical damage to structures
and life hazard
Numéro de référence
Reference number
CEI/IEC 62305-3:2006
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62305-3 © IEC:2006
–3–
CONTENTS
FOREWORD......................................................................................................................... 11
INTRODUCTION................................................................................................................... 15
1
Scope ............................................................................................................................. 17
2
Normative references ..................................................................................................... 17
3
Terms and definitions ..................................................................................................... 19
4
Lightning protection system (LPS) .................................................................................. 25
5
4.1 Class of LPS ......................................................................................................... 25
4.2 Design of the LPS ................................................................................................. 27
4.3 Continuity of steelwork in reinforced concrete structures ....................................... 27
External lightning protection system ............................................................................... 29
6
5.1 General ................................................................................................................. 29
5.2 Air-termination systems ......................................................................................... 29
5.3 Down-conductor systems....................................................................................... 37
5.4 Earth-termination system....................................................................................... 43
5.5 Components .......................................................................................................... 47
5.6 Materials and dimensions ...................................................................................... 51
Internal lightning protection system ................................................................................ 57
7
6.1 General ................................................................................................................. 57
6.2 Lightning equipotential bonding ............................................................................. 57
6.3 Electrical insulation of the external LPS ................................................................ 63
Maintenance and inspection of an LPS ........................................................................... 65
8
7.1 Application of inspections ...................................................................................... 65
7.2 Order of inspections .............................................................................................. 65
7.3 Maintenance.......................................................................................................... 65
Protection measures against injury to living beings due to touch and step voltages ........ 67
8.1
8.2
Protection measures against touch voltages .......................................................... 67
Protection measures against step voltages ............................................................ 67
Annex A (normative) Positioning the air-termination system ................................................. 69
Annex B (normative) Minimum cross-section of the entering cable screen in order to
avoid dangerous sparking ..................................................................................................... 81
Annex C (informative) Partitioning of the lightning current amongst down-conductors .......... 83
Annex D (informative) Additional information for LPS in the case of structures with a
risk of explosion.................................................................................................................... 91
Annex E (informative) Guidelines for the design, construction, maintenance and
inspection of lightning protection systems ........................................................................... 103
Bibliography........................................................................................................................ 307
62305-3 © IEC:2006
–5–
Figure 1 – Loop in a down-conductor .................................................................................... 39
Figure 2 – Minimum length l 1 of each earth electrode according to the class of LPS ............. 43
Figure A.1 – Volume protected by a vertical air-termination rod ............................................ 69
Figure A.2 – Volume protected by a vertical air-termination rod ............................................ 71
Figure A.3 – Volume protected by a wire air-termination system ........................................... 71
Figure A.4 – Volume protected by isolated wires combined in a mesh according to the
protective angle method and rolling sphere method .............................................................. 73
Figure A.5 – Volume protected by non-isolated wires combined in a mesh according to
the mesh method and the protective angle method ............................................................... 75
Figure A.6 – Design of an air-termination system according to the rolling sphere
method ................................................................................................................................. 77
Figure C.1 – Values of coefficient k c in the case of a wire air-termination system and a
type B earth-termination system............................................................................................ 85
Figure C.2 – Values of coefficient k c in the case of a mesh air-termination system and
type B earth-termination system............................................................................................ 87
Figure C.3 – Examples of calculation of the separation distance in the case of a
meshed air-termination system, an interconnecting ring of the down-conductors at
each level and a type B earth-termination system ................................................................. 89
Figure E.1 – LPS design flow diagram ................................................................................ 107
Figure E.2 – Values of coefficient k c in case of a sloped roof with air-termination on
the ridge and a type B earthing system ............................................................................... 121
Figure E.3 – LPS design for a cantilevered part of a structure............................................. 123
Figure E.4 – Equipotential bonding in a structure with a steel reinforcement ....................... 127
Figure E.5 – Welded joints of reinforcing rods in reinforced concrete, if permitted............... 129
Figure E.6 – Example of clamps used as joints between reinforcing rods and
conductors .......................................................................................................................... 131
Figure E.7 – Examples for connection points to the reinforcement in a reinforced
concrete wall ...................................................................................................................... 133
Figure E.8 – Use of metallic facade as natural down-conductor system and connection
of facade supports .............................................................................................................. 141
Figure E.9 – Connection of the continuous strip windows to a metal façade covering .......... 143
Figure E.10 – Internal down-conductors in industrial structures........................................... 149
Figure E.11– Installation of bonding conductors in reinforced concrete structures and
flexible bonds between two reinforced concrete parts ......................................................... 153
Figure E.12 – Protective angle method air-termination design for different heights
according to Table 2 ........................................................................................................... 161
Figure E.13 – Isolated external LPS using two isolated air-termination masts designed
according to the protective angle air-termination design method ......................................... 163
Figure E.14 – Isolated external LPS using two isolated air-termination masts,
interconnected by horizontal catenary wire ......................................................................... 165
Figure E.15 – Example of design of an air-termination of a non-isolated LPS by airtermination rods .................................................................................................................. 167
Figure E.16 – Example of design of an air-termination of a non isolated LPS by a
horizontal wire according to the protective angle air-termination design method ................. 169
Figure E.17 – Protected volume of an air- termination rod or mast on a sloped surface....... 171
62305-3 © IEC:2006
–7–
Figure E.18 – Design of an LPS air-termination according to the rolling sphere method,
protective angle method, mesh method and general arrangement of air-termination
elements ............................................................................................................................. 175
Figure E.19 – Design of an LPS air-termination conductor network on a structure with
complicated shape .............................................................................................................. 177
Figure E.20 – Space protected by two parallel air-termination horizontal wires or two
air-termination rods (r > h t )................................................................................................. 179
Figure E.21 – Points at which lightning will strike a building ................................................ 183
Figure E.22 – Example of design of non-isolated LPS air-termination according to the
mesh method air-termination design ................................................................................... 191
Figure E.23 – Some examples of details of an LPS on a structure with sloped tiled roofs.... 197
Figure E.24 – Construction of an LPS using natural components on the roof of the
structure ............................................................................................................................. 201
Figure E.25 – Positioning of the external LPS on a structure made of insulating
material e.g. wood or bricks with a height up to 60 m with flat roof and with roof fixtures .... 203
Figure E.26 – Construction of air-termination network on a roof with conductive
covering where puncturing of the covering is not acceptable ............................................... 205
Figure E.27 – Construction of external LPS on a structure of steel-reinforced concrete
using the reinforcement of the outer walls as natural components ....................................... 207
Figure E.28 – Example of an air-termination stud used on car park roofs ............................ 209
Figure E.29 – Air-termination rod used for protection of a metallic roof fixture with
electric power installations which are not bonded to the air-termination system .................. 211
Figure E.30 – Method of achieving electrical continuity on metallic parapet cladding .......... 213
Figure E.31 – Metallic roof fixture protected against direct lightning interception,
connected to air-termination system.................................................................................... 219
Figure E.32 – Example of construction of lightning protection of a house with a TV
antenna using the mast as an air-termination rod................................................................ 223
Figure E.33 – Installation of lightning protection of metallic equipment on a roof against
a direct lightning flash ......................................................................................................... 225
Figure E.34 – Connection of natural air-termination rod to air-termination conductor........... 229
Figure E.35 – Construction of the bridging between the segments of the metallic
façade plates ...................................................................................................................... 231
Figure E.36 – Installation of external LPS on a structure of isolating material with
different roof levels ............................................................................................................. 235
Figure E.37 – Examples of geometry of LPS conductors ..................................................... 237
Figure E.38 – Construction of an LPS using only two down-conductors and foundation
earth electrodes .................................................................................................................. 239
Figure E.39 – Examples of connection of earth termination to the LPS of structures
using natural down-conductors (girders) and detail of a test joint ........................................ 247
Figure E.40 – Construction of foundation earth ring for structures of different
foundation design ............................................................................................................... 255
Figure E.41 – Examples of two vertical electrodes in type A earthing arrangement ............. 259
Figure E.42 – Meshed earth termination system of a plant .................................................. 267
62305-3 © IEC:2006
–9–
Figure E.43 – Examples of separation distance between the LPS and metal
installations ........................................................................................................................ 279
Figure E.44 – Directions for calculations of the separation distance s for a worst case
lightning interception point at a distance l from the reference point according to 6.3 ........... 281
Figure E.45 – Example of an equipotential bonding arrangement ....................................... 287
Figure E.46 – Example of bonding arrangement in a structure with multiple point
entries of external conductive parts using a ring electrode for interconnection of
bonding bars ....................................................................................................................... 289
Figure E.47 – Example of bonding in the case of multiple point entries of external
conductive parts and an electric power or communication line using an internal ring
conductor for interconnection of the bonding bars ............................................................... 291
Figure E.48 – Example of bonding arrangement in a structure with multiple point
entries of external conductive parts entering the structure above ground level .................... 293
Table 1 – Relation between lightning protection levels (LPL) and class of LPS (see
IEC 62305-1) ........................................................................................................................ 25
Table 2 – Maximum values of rolling sphere radius, mesh size and protection angle
corresponding to the class of LPS......................................................................................... 31
Table 3 – Minimum thickness of metal sheets or metal pipes in air-termination systems ....... 35
Table 4 – Typical values of the distance between down-conductors and between ring
conductors according to the class of LPS.............................................................................. 39
Table 5 – LPS materials and conditions of use...................................................................... 49
Table 6 – Material, configuration and minimum cross-sectional area of air-termination
conductors, air-termination rods and down-conductors.......................................................... 53
Table 7 – Material, configuration and minimum dimensions of earth electrodes..................... 55
Table 8 – Minimum dimensions of conductors connecting different bonding bars or
connecting bonding bars to the earth-termination system ...................................................... 59
Table 9 – Minimum dimensions of conductors connecting internal metal installations to
the bonding bar..................................................................................................................... 59
Table 10 – Isolation of external LPS – Values of coefficient k i .............................................. 63
Table 11 – Isolation of external LPS – Values of coefficient k c .............................................. 63
Table 12 – Isolation of external LPS – Values of coefficient k m ............................................. 65
Table B.1 – Cable length to be considered according to the condition of the screen.............. 81
Table C.1 – Values of coefficient k c ...................................................................................... 83
Table E.1 – Suggested fixing centres .................................................................................. 193
Table E.2 – Maximum period between inspections of an LPS .............................................. 297
62305-3 © IEC:2006
– 11 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
PROTECTION AGAINST LIGHTNING –
Part 3: Physical damage to structures and life hazard
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC national committees). The object of the IEC is to promote
international cooperation on all questions concerning standardization in the electrical and electronic fields. To
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closely with the International Organization for Standardization (ISO) in accordance with conditions determined
by agreement between the two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested IEC national committees.
3) IEC publications have the form of recommendations for international use and are accepted by IEC national
committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
publications is accurate, the IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC national committees undertake to apply IEC publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to the IEC or its directors, employees, servants or agents including individual experts
and members of its technical committees and IEC national committees for any personal injury, property damage
or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC publication or any other IEC
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8) Attention is drawn to the normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC publication may be the subject of
patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International standard IEC 62305-3 has been prepared by IEC technical committee 81:
Lightning protection.
The IEC 62305 series (Parts 1 to 5), is produced in accordance with the new Publications`
Plan, approved by National Committees (81/171/RQ (2001-06-29)), which restructures in a
more simple and rational form and updates the Publications of the IEC 61024 series, the IEC
61312 series and the IEC 61663 series.
The text of this first edition of IEC 62305-3 is compiled from and replaces
–
IEC 61024-1, first edition (1990).
–
IEC 61024-1-2, first edition (1998).
62305-3 © IEC:2006
– 13 –
The text of this standard is based on the following documents:
FDIS
Report on voting
81/264/FDIS
81/269/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above Table.
This publication has been drafted, as close as possible, in accordance with the ISO/IEC
Directives, Part 2.
IEC 62305 consists of the following parts, under the general title Protection against lightning:
Part 1: General principles
Part 2: Risk management
Part 3: Physical damage to structures and life hazard
Part 4: Electrical and electronic systems within structures
Part 5: Services 1
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC website "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be:
•
•
•
•
reconfirmed;
withdrawn;
replaced by a revised edition; or
amended.
In the United States, based on the requirements of NFPA 780: Standard for the Installation of Lightning Protection
Systems 2004 Edition and practical experience in the use of horizontal earth electrodes, the minimum length of
horizontal earth electrodes is not required to be twice that required for vertical electrodes.
In France, Portugal and Spain:
–
natural components cannot
complete/enhance the LPS;
substitute
as
lightning
protection
components
–
aluminium solid round diameters should be extended from 8 mm to 10 mm;
–
stranded conductors cannot be used as down-conductors;
but
–
diameter of solid round conductors should be extended from 16 mm to 18 mm;
–
hot dip galvanized steel solid tape thickness should be extended from 2 mm to 3,5 mm.
———————
1 To be published
may
be
used
to
62305-3 © IEC:2006
– 15 –
INTRODUCTION
This part of IEC 62305 deals with the protection, in and around a structure, against physical
damage and injury to living beings due to touch and step voltages.
The main and most effective measure for protection of structures against physical damage is
considered to be the lightning protection system (LPS). It usually consists of both external
and internal lightning protection systems.
An external LPS is intended to:
a) intercept a lightning flash to the structure (with an air-termination system);
b) conduct the lightning current safely towards earth (using a down-conductor system);
c) disperse the lightning current into the earth (using an earth-termination system).
An internal LPS prevents dangerous sparking within the structure using either equipotential
bonding or a separation distance (and hence electrical insulation) between the external LPS
(as defined in 3.2) components and other electrically conducting elements internal to the
structure.
Main protection measures against injury to living beings due to touch and step voltages are
intended to:
1) reduce the dangerous current flowing through bodies by insulating exposed conductive
parts, and/or by increasing the surface soil resistivity;
2) reduce the occurrence of dangerous touch and step voltages by physical restrictions
and/or warning notices.
The type and location of an LPS should be carefully considered in the initial design of a new
structure, thereby enabling maximum advantage to be taken of the electrically conductive
parts of the structure. By doing so, design and construction of an integrated installation is
made easier, the overall aesthetic aspects can be improved, and the effectiveness of the LPS
can be increased at minimum cost and effort.
Access to the ground and the proper use of foundation steelwork for the purpose of forming
an effective earth termination may well be impossible once construction work on a site has
commenced. Therefore, soil resistivity and the nature of the earth should be considered at the
earliest possible stage of a project. This information is fundamental to the design of an earthtermination system and may influence the foundation design work for the structure.
Regular consultation between LPS designers and installers, architects and builders is
essential in order to achieve the best result at minimum cost.
If lightning protection is to be added to an existing structure, every effort should be made to
ensure that it conforms to the principles of this standard. The design of the type and location
of an LPS should take into account the features of the existing structure.
62305-3 © IEC:2006
– 17 –
PROTECTION AGAINST LIGHTNING –
Part 3: Physical damage to structures and life hazard
1
Scope
This part of IEC 62305 provides the requirements for protection of a structure against physical
damage by means of a lightning protection system (LPS), and for protection against injury to
living beings due to touch and step voltages in the vicinity of an LPS (see IEC 62305-1).
This standard is applicable to:
a) design, installation, inspection and maintenance of an LPS for structures without limitation
of their height;
b) establishment of measures for protection against injury to living beings due to touch and
step voltages.
NOTE 1 Specific requirements for an LPS in structures dangerous to their surroundings due to the risk of explosion are
under consideration. Additional information is provided in Annex D for use in the interim.
NOTE 2 This part of IEC 62305 is not intended to provide protection against failures of electrical and electronic
systems due to overvoltages. Specific requirements for such cases are provided in IEC 62305-4.
2
Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60079-10:2002, Electrical apparatus
Classification of hazardous areas
for
explosive
gas
atmospheres
–
Part 10:
IEC 60079-14:2002, Electrical apparatus for explosive gas atmospheres – Part 14: Electrical
installations in hazardous areas (other than mines)
IEC 61241-10:2004, Electrical apparatus for use in the presence of combustible dust –
Part 10: Classification of areas where combustible dusts are or may be present
IEC 61241-14:2004, Electrical apparatus for use in the presence of combustible dust –
Part 14: Selection and installation
IEC 61643-12:2002, Low-voltage surge protective devices – Part 12: Surge protective devices
connected to low voltage power distribution systems – Selection and application principles
IEC 62305-1, Protection against lightning – Part 1: General principles
IEC 62305-2, Protection against lightning – Part 2: Risk management
IEC 62305-4, Protection against lightning – Part 4: Electrical and electronic systems within
structures
62305-3 © IEC:2006
– 19 –
IEC 62305-5, Protection against lightning – Part 5: Services 1
ISO 3864-1, Graphical symbols – Safety colours and safety signs – Part 1: Design principles
for safety signs in workplaces and public areas
3
Terms and definitions
For the purposes of this document, the following terms and definitions, some of which have
already been cited in Part 1 but are repeated here for ease of reference, as well as those
given in other parts of IEC 62305, apply.
3.1
lightning protection system
LPS
complete system used to reduce physical damage due to lightning flashes to a structure
NOTE
It consists of both external and internal lightning protection systems.
3.2
external lightning protection system
part of the LPS consisting of an air-termination system, a down-conductor system and an
earth-termination system
3.3
external LPS isolated from the structure to be protected
LPS with an air-termination system and down-conductor system positioned in such a way that
the path of the lightning current has no contact with the structure to be protected
NOTE
In an isolated LPS, dangerous sparks between the LPS and the structure are avoided.
3.4
external LPS not isolated from the structure to be protected
LPS with an air-termination system and down-conductor system positioned in such a way that
the path of the lightning current can be in contact with the structure to be protected
3.5
internal lightning protection system
part of the LPS consisting of lightning equipotential bonding and/or electrical insulation of
external LPS
3.6
air-termination system
part of an external LPS using metallic elements such as rods, mesh conductors or catenary
wires intended to intercept lightning flashes
3.7
down-conductor system
part of an external LPS intended to conduct lightning current from the air-termination system
to the earth-termination system
———————
1 To be published
62305-3 © IEC:2006
– 21 –
3.8
ring conductor
conductor forming a loop around the structure and interconnecting the down-conductors for
distribution of lightning current among them
3.9
earth-termination system
part of an external LPS which is intended to conduct and disperse lightning current into the
earth
3.10
earthing electrode
part or a group of parts of the earth-termination system which provides direct electrical
contact with the earth and disperses the lightning current into the earth
3.11
ring earthing electrode
earthing electrode forming a closed loop around the structure below or on the surface of the
earth
3.12
foundation earthing electrode
reinforcing steel of foundation or additional conductor embedded in the concrete foundation of
a structure and used as an earthing electrode
3.13
conventional earth impedance
ratio of the peak values of the earth-termination voltage and the earth-termination current
which, in general, do not occur simultaneously
3.14
earth-termination voltage
potential difference between the earth-termination system and the remote earth
3.15
natural component of LPS
conductive component installed not specifically for lightning protection which can be used in
addition to the LPS or in some cases could provide the function of one or more parts of the
LPS
NOTE
Examples of the use of this term include:
– natural air-termination;
– natural down-conductor;
– natural earthing electrode.
3.16
connecting component
part of an external LPS which is used for the connection of conductors to each other or to
metallic installations
3.17
fixing component
part of an external LPS which is used to fix the elements of the LPS to the structure to be
protected
62305-3 © IEC:2006
– 23 –
3.18
metal installations
extended metal items in the structure to be protected which may form a path for lightning
current, such as pipework, staircases, elevator guide rails, ventilation, heating and airconditioning ducts, and interconnected reinforcing steel
3.19
external conductive parts
extended metal items entering or leaving the structure to be protected such as pipework,
metallic cable elements, metal ducts, etc. which may carry a part of the lightning current
3.20
electrical system
system incorporating low voltage power supply components and possibly electronic
components
3.21
electronic system
system incorporating sensitive electronic components such as communication equipment,
computer, control and instrumentation systems, radio systems, power electronic installations
3.22
internal systems
electrical and electronic systems within a structure
3.23
lightning equipotential bonding
EB
bonding to the LPS of separated conductive parts, by direct connections or via surge
protective devices, to reduce potential differences caused by lightning current
3.24
bonding bar
metal bar on which metal installations, external conductive parts, electric power and telecommunication lines, and other cables can be bonded to an LPS
3.25
bonding conductor
conductor connecting separated conductive parts to LPS
3.26
interconnected reinforcing steel
steelwork within a concrete structure which is considered electrically continuous
3.27
dangerous sparking
electrical discharge due to lightning which causes physical damage in the structure to be
protected
3.28
separation distance
distance between two conductive parts at which no dangerous sparking can occur
62305-3 © IEC:2006
– 25 –
3.29
surge protective device
SPD
device that is intended to limit transient overvoltages and divert surge currents. It contains at
least one non-linear component
3.30
test joint
joint designed to facilitate electrical testing and measurement of LPS components
3.31
class of LPS
number denoting the classification of an LPS according to the lightning protection level for
which it is designed
3.32
lightning protection designer
specialist competent and skilled in the design of the LPS
3.33
lightning protection installer
person competent and skilled in the installation of the LPS
3.34
structures with risk of explosion
structures containing solid explosives materials or hazardous zones as determined in
accordance with IEC 60079-10 and IEC 61241-10
4
Lightning protection system (LPS)
4.1
Class of LPS
The characteristics of an LPS are determined by the characteristics of the structure to be
protected and by the considered lightning protection level.
Four classes of LPS (I to IV) are defined in this standard corresponding to lightning protection
levels defined in IEC 62305-1 (see Table 1).
Table 1 – Relation between lightning protection levels (LPL)
and class of LPS (see IEC 62305-1)
LPL
Class of LPS
I
I
II
II
III
III
IV
IV
Each class of LPS is characterized by the following.
a) Data dependent upon the class of LPS:
–
lightning parameters (see Tables 3 and 4 in IEC 62305-1);
–
rolling sphere radius, mesh size and protection angle (see 5.2.2);
–
typical distances between down-conductors and between ring conductors (see 5.3.3);
–
separation distance against dangerous sparking (see 6.3);
–
minimum length of earth electrodes (see 5.4.2).
62305-3 © IEC:2006
– 27 –
b) Data not dependent upon the class of LPS:
–
lightning equipotential bonding (see 6.2);
–
minimum thickness of metal sheets or metal pipes in air-termination systems (see
5.2.5);
–
LPS materials and conditions of use (see 5.5);
–
material, configuration and minimum dimensions for air-terminations, down-conductors
and earth-terminations (see 5.6);
–
minimum dimensions of connecting conductors (see 6.2.2).
Performance of each class of LPS is given in Annex B of IEC 62305-2.
The class of required LPS shall be selected on the basis of a risk assessment (see IEC 62305-2).
4.2
Design of the LPS
A technically and economically optimized design of an LPS is possible especially if the steps
in the design and construction of the LPS are coordinated with the steps in the design and
construction of the structure to be protected. In particular, the design of the structure itself
should utilize the metal parts of the structure as parts of the LPS.
The design of the class and location of the LPS for existing structures shall take into account
the constraints of the existing situation.
The design documentation of an LPS shall contain all the information necessary to ensure
correct and complete installation. For detailed information, see Annex E.
4.3
Continuity of steelwork in reinforced concrete structures
Steelwork within reinforced concrete structures is considered to be electrically continuous
provided that the major part of interconnections of vertical and horizontal bars are welded or
otherwise securely connected. Connections of vertical bars shall be welded, clamped or
overlapped a minimum of 20 times their diameters and bound or otherwise securely
connected. For new structures, the connections between reinforcement elements shall be
specified by the designer or installer, in cooperation with the builder and the civil engineer.
For structures utilizing steel reinforced concrete (including pre-cast, pre-stressed reinforced
units), the electrical continuity of the reinforcing bars shall be determined by electrical testing
between the uppermost part and ground level. The overall electrical resistance should not be
greater than 0,2 Ω, measured using test equipment suitable for this purpose. If this value is
not achieved, or it is not practical to conduct such testing, the reinforcing steel shall not be
used as a natural down-conductor as discussed in 5.3.5. In this case it is recommended that
an external down-conductor be installed: In the case of structures of pre-cast reinforced
concrete, the electrical continuity of the reinforcing steel shall be established between
individual adjacent pre-cast concrete units.
NOTE 1
For further information on the continuity of steelwork in reinforced concrete structures, see Annex E.
NOTE 2
In several countries, the use of reinforced concrete as a part of the LPS is not allowed.
62305-3 © IEC:2006
5
– 29 –
External lightning protection system
5.1
5.1.1
General
Application of an external LPS
The external LPS is intended to intercept direct lightning flashes to the structure, including
flashes to the side of the structure, and conduct the lightning current from the point of strike to
ground. The external LPS is also intended to disperse this current into the earth without
causing thermal or mechanical damage, nor dangerous sparking which may trigger fire or
explosions.
5.1.2
Choice of external LPS
In most cases, the external LPS may be attached to the structure to be protected.
An isolated external LPS should be considered when the thermal and explosive effects at the
point of strike, or on the conductors carrying the lightning current, may cause damage to the
structure or to the contents (see Annex E). Typical examples include structures with
combustible covering, structures with combustible walls and areas at risk of explosion and
fire.
NOTE The use of an isolated LPS may be convenient where it is predicted that changes in the structure, its
contents or its use will require modifications to the LPS.
An isolated external LPS may also be considered when the susceptibility of the contents
warrants the reduction of the radiated electromagnetic field associated with the lightning
current pulse in the down-conductor.
5.1.3
Use of natural components
Natural components made of conductive materials, which will always remain in/on the
structure and will not be modified (e.g. interconnected reinforced steel, metal framework of
the structure, etc.) may be used as parts of an LPS.
Other natural components should be considered as being additional to an LPS.
NOTE
5.2
5.2.1
For further information, see Annex E.
Air-termination systems
General
The probability of structure penetration by a lightning current is considerably decreased by
the presence of a properly designed air-termination system.
Air-termination systems can be composed of any combination of the following elements:
a) rods (including free-standing masts);
b) catenary wires;
c) meshed conductors.
To conform to this standard, all types of air-termination systems shall be positioned in
accordance with 5.2.2, 5.2.3 and Annex A.
62305-3 © IEC:2006
– 31 –
The individual air-termination rods should be connected together at roof level to ensure
current division.
Radioactive air terminals are not allowed.
5.2.2
Positioning
Air-termination components installed on a structure shall be located at corners, exposed
points and edges (especially on the upper level of any facades) in accordance with one or
more of the following methods.
Acceptable methods to be used in determining the position of the air-termination system
include:
–
the protection angle method;
–
the rolling sphere method;
–
the mesh method.
The rolling sphere method is suitable in all cases.
The protection angle method is suitable for simple-shaped buildings but it is subject to limits
of air-termination height indicated in Table 2.
The mesh method is a suitable form of protection where plane surfaces are to be protected.
The values for the protection angle, rolling sphere radius and mesh size for each class of LPS
are given in Table 2. Detailed information on the positioning of the air-termination system is
given in Annex A.
Table 2 – Maximum values of rolling sphere radius, mesh size
and protection angle corresponding to the class of LPS
Protection method
Class of LPS
Rolling sphere radius r
m
Mesh size W
m
I
20
5×5
II
30
10 × 10
III
45
15 × 15
IV
60
20 × 20
Protection angle
α°
See figure below
62305-3 © IEC:2006
α °
– 33 –
80
70
60
50
Class of
LPS
40
30
20
IV
III
II
I
10
0
0
2
10
20
30
40
50
H m
60
IEC 2095/05
NOTE 1 Not applicable beyond the values marked with •.
Only rolling sphere and mesh methods apply in these cases.
NOTE 2
H is the height of air-termination above the reference plane of the area to be protected.
NOTE 3
The angle will not change for values of H below 2 m.
5.2.3
Air-terminations against flashes to the side of tall structures
On structures taller than 60 m, flashes to the side may occur, especially to points, corners
and edges of surfaces.
NOTE In general the risk due to these flashes is low because only a few per cent of all flashes to tall structures
will be to the side and moreover their parameters are significantly lower than those of flashes to the top of
structures. However, electrical and electronic equipment on walls outside structures may be destroyed even by
lightning flashes with low current peak values.
An air-termination system shall be installed to protect the upper part of tall structures (i.e.
typically the topmost 20 % of the height of the structure) and the equipment installed on it
(see Annex A).
The rules for positioning air-termination systems on roofs shall also apply to those upper parts
of structures.
In addition, for structures taller than 120 m, all parts which may be endangered above 120 m
should be protected.
5.2.4
Construction
Air-terminations of an LPS not isolated from the structure to be protected may be installed as
follows:
–
if the roof is made of non-combustible material the air-termination conductors may be
positioned on the surface of the roof;
–
if the roof is made of readily-combustible material, due care needs to be taken with regard
to the distance between the air-termination conductors and the material. For thatched
roofs where no steel bars are used for monitoring of the reed, a distance of 0,15 m is
adequate. For other combustible materials a distance not lower than 0,10 m is considered
adequate;
62305-3 © IEC:2006
–
– 35 –
Easily-combustible parts of the structure to be protected shall not remain in direct contact
with the components of an external LPS and shall not remain directly under any metallic
roofing membrane that might be punctured by a lightning flash (see 5.2.5).
Account shall also be taken of less combustible membranes such as wooden sheets.
NOTE If it is likely that water may accumulate on a flat roof, air-terminations should be installed above the
maximum probable water level.
5.2.5
Natural components
The following parts of a structure should be considered as natural air-termination components
and part of an LPS in accordance with 5.1.3.
a) Metal sheets covering the structure to be protected provided that:
–
the electrical continuity between the various parts is made durable (e.g. by means of
brazing, welding, crimping, seaming, screwing or bolting);
–
the thickness of the metal sheet is not less than the value t’ given in Table 3 if it is not
important to prevent puncture of the sheeting or to consider ignition of any readilycombustible materials underneath;
–
the thickness of the metal sheet is not less than the value t given in Table 3 if it is
necessary to take precautions against puncture or to consider hot spot problems;
–
they are not clad with insulating material.
Table 3 – Minimum thickness of metal sheets or metal pipes in air-termination systems
Class of LPS
I to IV
Material
Thickness
t
mm
a
Thickness
t′
mm
Lead
–
2,0
Steel (stainless,
galvanized)
4
0,5
Titanium
4
0,5
Copper
5
0,5
Aluminium
7
0,65
Zinc
–
0,7
b
a
t prevents puncture, hot spot or ignition.
b
t ′ only for metal sheets if it is not important to prevent puncture, hot spot or ignition
problems.
b) Metal components of roof construction (trusses, interconnected reinforcing steel, etc.),
underneath non-metallic roofing, provided that this latter part can be excluded from the
structure to be protected.
c) Metal parts such as ornamentation, railings, pipes, coverings of parapets, etc., with crosssections not less than that specified for standard air-termination components.
d) Metal pipes and tanks on the roof, provided that they are constructed of material with
thicknesses and cross-sections in accordance with Table 6.
e) Metal pipes and tanks carrying readily-combustible or explosive mixtures, provided that
they are constructed of material with thickness not less than the appropriate value of t
given in Table 3 and that the temperature rise of the inner surface at the point of strike
does not constitute a danger (for detailed information, see Annex E).
62305-3 © IEC:2006
– 37 –
If the conditions for thickness are not fulfilled, the pipes and tanks shall be integrated into the
structure to be protected.
Piping carrying readily-combustible or explosive mixtures shall not be considered as an airtermination natural component if the gasket in the flange couplings is not metallic or if the
flange-sides are not otherwise properly bonded.
NOTE A thin coating of protective paint or about 1 mm asphalt or 0,5 mm PVC is not regarded as an insulator.
Detailed information is given in Annex E.
5.3
Down-conductor systems
5.3.1
General
In order to reduce the probability of damage due to lightning current flowing in the LPS, the
down-conductors shall be arranged in such a way that from the point of strike to earth:
a) several parallel current paths exist;
b) the length of the current paths is kept to a minimum;
c) equipotential bonding to conducting parts of the structure is performed according to the
requirements of 6.2.
NOTE 1 Lateral connection of down-conductors at ground level and every 10 m to 20 m of height, in accordance
with Table 4, is considered to be good practice.
The geometry of the down-conductors and of the ring conductors affects the separation
distance (see 6.3).
NOTE 2 The installation of as many down-conductors as possible, at equal spacing around the perimeter
interconnected by ring conductors, reduces the probability of dangerous sparking and facilitates the protection of
internal installations (see IEC 62305-4). This condition is fulfilled in metal framework structures and in reinforced
concrete structures in which the interconnected steel is electrically continuous.
Typical values of the distance between down-conductors and between horizontal ring conductors are given in
Table 4.
More information on partitioning of the lightning current amongst down-conductors is given in Annex C.
5.3.2
Positioning for an isolated LPS
a) If the air-termination consists of rods on separate masts (or one mast) not made of metal
or interconnected reinforcing steel, at least one down-conductor is needed for each mast.
No additional down-conductors are required for masts made of metal or interconnected
reinforcing steel.
NOTE
In several countries, the use of reinforced concrete as a part of the LPS is not allowed.
b) If the air-termination consists of catenary wires (or one wire), at least one down-conductor
is needed at each supporting structure.
c) If the air-termination forms a network of conductors, one down-conductor is needed at
least at each supporting wire end.
5.3.3
Positioning for a non-isolated LPS
For each non-isolated LPS the number of down-conductors shall be not less than two and
should be distributed around the perimeter of the structure to be protected, subject to
architectural and practical constraints.
62305-3 © IEC:2006
– 39 –
An equal spacing of the down-conductors is preferred around the perimeter. Typical values of
the distance between down-conductors are given in Table 4.
NOTE
The value of the distance between down-conductors is correlated with the separation distance given in 6.3.
Table 4 – Typical values of the distance between down-conductors
and between ring conductors according to the class of LPS
Class of LPS
Typical distances
m
I
10
II
10
III
15
IV
20
A down-conductor should be installed at each exposed corner of the structure, where this is
possible.
5.3.4
Construction
The down-conductors shall be installed so that, as far as practicable, they form a direct
continuation of the air-termination conductors.
Down-conductors shall be installed straight and vertical such that they provide the shortest
and most direct path to earth. The formation of loops shall be avoided, but where this is not
possible, the distance s, measured across the gap between two points on the conductor and
the length l of the conductor between those points (see Figure 1) shall conform to 6.3.
l1
s
l2
l3
l = l1 + l2 + l3
IEC 2096/05
Figure 1 – Loop in a down-conductor
Down-conductors shall not be installed in gutters or down-spouts even if they are covered by
insulating material.
NOTE The effects of moisture in the gutters lead to intensive corrosion of the down-conductor. It is recommended
that the down-conductors be positioned such that a separation distance in accordance with 6.3 is provided between
them and any doors and windows.
62305-3 © IEC:2006
– 41 –
Down-conductors of an LPS not isolated from the structure to be protected may be installed
as follows:
–
if the wall is made of non-combustible material, the down-conductors may be positioned
on the surface or in the wall;
–
if the wall is made of readily-combustible material the down-conductors may be positioned
on the surface of the wall, provided that their temperature rise due to the passage of
lightning current is not dangerous for the material of the wall;
–
if the wall is made of readily-combustible material and the temperature rise of downconductors is dangerous, the down-conductors shall be placed in such a way that the
distance between them and the wall is always greater than 0,1 m. Mounting brackets may
be in contact with the wall.
When the distance from down-conductor to a combustible material cannot be assured, the
cross-section of the conductor shall be not less than 100 mm 2 .
5.3.5
Natural components
The following parts of the structure should be considered as natural down-conductors:
a) the metal installations provided that
–
the electrical continuity between the various parts is made durable in accordance with
5.5.2,
–
their dimensions are at least equal to that specified in Table 6 for standard downconductors.
Piping carrying readily-combustible or explosive mixtures shall not be considered as a
down-conductor natural component if the gasket in the flange couplings is not metallic or if
the flange-sides are not otherwise properly bonded.
NOTE 1
Metal installations may be clad with insulating material.
b) the metal of the electrically-continuous reinforced concrete framework of the structure;
NOTE 2 With prefabricated reinforced concrete, it is important to establish interconnection points between
the reinforcing elements. It is also important that reinforced concrete contains a conductive connection
between the interconnection points. The individual parts should be connected on-site during assembly (see
Annex E).
NOTE 3 In the case of pre-stressed concrete, attention should be paid to the risk of causing unacceptable
mechanical consequences, due either to lightning current or as a result of the connection to the lightning
protection system.
c) the interconnected steel framework of the structure;
NOTE 4 Ring conductors are not necessary if the metal framework of steel structures or the interconnected
reinforcing steel of the structure is used as down-conductors.
d) the facade elements, profile rails and metallic sub-constructions of facades, provided that
–
their dimensions conform to the requirements for down-conductors (see 5.6.2) and that
for metal sheets or metal pipes thicknesses shall be not less than 0,5 mm,
–
their electrical continuity in a vertical direction conforms to the requirements of 5.5.2.
NOTE 5
5.3.6
For more information, see Annex E.
Test joints
At the connection of the earth termination, a test joint should be fitted on each downconductor, except in the case of natural down-conductors combined with foundation earth
electrodes.
For measuring purposes, the joint shall be capable of being opened with the aid of a tool. In
normal use it shall remain closed.
62305-3 © IEC:2006
5.4
– 43 –
Earth-termination system
5.4.1
General
When dealing with the dispersion of the lightning current (high frequency behaviour) into the
ground, whilst minimizing any potentially dangerous overvoltages, the shape and dimensions
of the earth-termination system are the important criteria. In general, a low earthing
resistance (if possible lower than 10 Ω when measured at low frequency) is recommended.
From the viewpoint of lightning protection, a single integrated structure earth-termination
system is preferable and is suitable for all purposes (i.e. lightning protection, power systems
and telecommunication systems).
Earth-termination systems shall be bonded in accordance with the requirements of 6.2.
NOTE 1 The conditions of separation and bonding of other earth-termination systems are usually determined by
the appropriate national authorities.
NOTE 2 Serious corrosion problems can occur when earthing systems made of different materials are connected
to each other.
5.4.2
Earthing arrangement in general conditions
For earth-termination systems, two basic types of earth electrode arrangements apply.
5.4.2.1
Type A arrangement
This type of arrangement comprises horizontal or vertical earth electrodes installed outside
the structure to be protected connected to each down-conductor.
In type A arrangements, the total number of earth electrodes shall be not less than two.
100
90
80
Class I
70
l1 m
60
50
Class II
40
30
20
10
Class III-IV
0
0
500
1 000
1 500
ρ Ωm
NOTE
2 000
2 500
3 000
IEC 2097/05
Classes III and IV are independent of soil resistivity.
Figure 2 – Minimum length l 1 of each earth electrode according to the class of LPS
62305-3 © IEC:2006
– 45 –
The minimum length of each earth electrode at the base of each down-conductor is
–
l1
for horizontal electrodes, or
–
0,5 l 1
for vertical (or inclined) electrodes,
where l 1 is the minimum length of horizontal electrodes shown in the relevant part of Figure 2.
For combined (vertical or horizontal) electrodes, the total length shall be considered.
The minimum lengths stated in Figure 2 may be disregarded provided that an earthing
resistance of the earth-termination system less than 10 Ω (measured at a frequency different
from the power frequency and its multiple in order to avoid interference) is achieved.
NOTE 1
Reduction of earthing resistance by the extension of earth electrodes is practically possible up to 60 m.
NOTE 2
For further information, refer to Annex E.
5.4.2.2
Type B arrangement
This type of arrangement comprises either a ring conductor external to the structure to be
protected, in contact with the soil for at least 80 % of its total length, or a foundation earth
electrode. Such earth electrodes may also be meshed.
For the ring earth electrode (or foundation earth electrode), the mean radius r e of the area
enclosed by the ring earth electrode (or foundation earth electrode) shall be not less than the
value l 1 :
re ≥ l1
(1)
where l 1 is represented in Figure 2 according to LPS class I, II, III and IV.
When the required value of l 1 is larger than the convenient value of r e , additional horizontal or
vertical (or inclined) electrodes shall be added with individual lengths l r (horizontal) and l v
(vertical) given by the following equations:
and
lr = l1 – re
(2)
l v = (l 1 – r e )/2
(3)
It is recommended that the number of electrodes shall be not less than the number of the
down-conductors, with a minimum of two.
The additional electrodes should be connected to the ring earth electrode at points where the
down-conductors are connected and, for as many as possible, equidistantly.
5.4.3
Installation of earth electrodes
The ring earth electrode (type B arrangement) should preferably be buried at a depth of at
least 0,5 m and at a distance of about 1 m around the external walls.
The earth electrodes (type A arrangement) shall be installed at a depth of upper end at least
0,5 m and distributed as uniformly as possible to minimize electrical coupling effects in the
earth.
62305-3 © IEC:2006
– 47 –
Earth electrodes shall be installed in such a way as to allow inspection during construction.
The embedded depth and the type of earth electrodes shall be such as to minimize the effects
of corrosion, soil drying and freezing and thereby stabilize the conventional earth resistance.
It is recommended that the upper part of a vertical earth electrode equal to the depth of
freezing soil should not be regarded as being effective under frost conditions.
NOTE Hence, for every vertical electrode, 0,5 m should be added to the value of the length l 1 , calculated in
5.4.2.1 and 5.4.2.2.
For bare solid rock, only type B earthing arrangement is recommended.
For structures with extensive electronic systems or with high risk of fire (see IEC 62305-2),
type B earthing arrangement is preferable.
5.4.4
Natural earth electrodes
Interconnected reinforcing steel in concrete foundations in accordance with 5.6, or other
suitable underground metal structures, should preferably be used as an earth electrode.
When the metallic reinforcement in concrete is used as an earth electrode, special care shall
be exercised at the interconnections to prevent mechanical splitting of the concrete.
NOTE 1 In the case of pre-stressed concrete, consideration should be given to the consequences of the passage
of lightning discharge currents which may produce unacceptable mechanical stresses.
NOTE 2
If a foundation earth electrode is used, a long-term increase in earthing resistance is possible.
NOTE 3
More extensive information on this topic is reported in Annex E.
5.5
Components
Components of an LPS shall withstand the electromagnetic effects of lightning current and
predictable accidental stresses without being damaged.
Components of an LPS shall be manufactured from the materials listed in Table 5 or from
other materials with equivalent mechanical, electrical and chemical (corrosion) performance
characteristics.
NOTE
Components made of material other than metal may be used for fixing.
62305-3 © IEC:2006
– 49 –
Table 5 – LPS materials and conditions of use
Use
Material
Copper
In open air
In earth
Corrosion
In concrete
Solid
Solid
Solid
Stranded
Stranded
Stranded
As coating
As coating
Solid
Solid
Hot
galvanized
steel
Solid
Stainless
steel
Solid
Solid
Solid
Stranded
Stranded
Stranded
Aluminium
Solid
Unsuitable
Solid
Solid
As coating
As Coating
Stranded
Good in many
environments
Increased by
Sulphur
compounds
–
Organic
materials
Acceptable in air,
in concrete and in
benign soil
High chlorides
content
Good in many
environments
High chlorides
content
Unsuitable
Good in
atmospheres
containing low
concentrations of
sulphur and
chloride
Alkaline
solutions
Copper
Unsuitable
Good in
atmosphere with
high
concentration of
sulphates
Acid soils
Copper
Stranded
Stranded
Lead
Resistance
May be
destroyed
by
galvanic
coupling
with
Copper
–
Stainless
steel
NOTE 1 This table gives general guidance only. In special circumstances more careful corrosion immunity
considerations are required (see Annex E).
NOTE 2 Stranded conductors are more vulnerable to corrosion than solid conductors. Stranded conductors are
also vulnerable where they enter or exit earth/concrete positions. This is the reason why stranded galvanized steel
is not recommended in earth.
NOTE 3
Galvanized steel may be corroded in clay soil or moist soil.
NOTE 4 Galvanized steel in concrete should not extend into the soil due to possible corrosion of the steel just
outside the concrete.
NOTE 5 Galvanized steel in contact with reinforcement steel in concrete may, under certain circumstances, cause
damage to the concrete.
NOTE 6
5.5.1
Use of lead in the earth is often banned or restricted due to environmental concerns.
Fixing
Air-terminations and down-conductors shall be firmly fixed so that the electrodynamic or
accidental mechanical forces (for instance vibrations, slipping of slabs of snow, thermal
expansion, etc.) will not cause conductors to break or loosen (see Annex D of IEC 62305-1).
5.5.2
Connections
The number of connections along the conductors shall be kept to a minimum. Connections
shall be made secure by such means as brazing, welding, clamping, crimping, seaming,
screwing or bolting.
Connections of steelwork within reinforced concrete structures shall conform to 4.3.
62305-3 © IEC:2006
5.6
5.6.1
– 51 –
Materials and dimensions
Materials
Material and its dimensions shall be chosen bearing in mind the possibility of corrosion either
of the structure to be protected or of the LPS.
5.6.2
Dimensions
Configurations and minimum cross-sectional areas of air-termination conductors, airtermination rods and down-conductors are given in Table 6.
Configurations and minimum dimensions of earth electrodes are given in Table 7.
62305-3 © IEC:2006
– 53 –
Table 6 – Material, configuration and minimum cross-sectional area of air-termination
conductors, air-termination rods and down-conductors
Material
Configuration
Minimum crosssectional area
Comments
10)
mm 2
Copper
Solid tape
Solid round
7)
Stranded
Solid round
Tin plated copper
1)
3), 4)
Solid tape
Solid round
7)
Stranded
Aluminium
Solid tape
Aluminium alloy
50
8 mm diameter
50
8)
1,7 mm min. diameter of each strand
8)
200
16 mm diameter
50
8)
2 mm min. thickness
50
8)
8 mm diameter
50
8)
1,7 mm min. diameter of each strand
3 mm min. thickness
Solid round
50
Stranded
50
8)
1,7 mm min. diameter of each strand
Solid tape
50
8)
2,5 mm min. thickness
50
50
Solid round
3)
Solid tape
9)
Solid round
Solid tape
3), 4), 9)
6)
Solid round
6)
Solid round
3), 4)
8)
8)
200 8)
50
8)
50
70
Stranded
8)
50
50
8 mm diameter
8 mm diameter
8)
200
50
Solid round
Stranded
Stainless steel
2 mm min. thickness
8)
8)
Stranded
5)
8)
70
Solid round
Hot dipped galvanized
steel 2)
50
8)
200 8)
1,7 mm min. diameter of each strand
16 mm diameter
2,5 mm min. thickness
8 mm diameter
1,7 mm min. diameter of each strand
16 mm diameter
2 mm min. thickness
8 mm diameter
1,7 mm min. diameter of each strand
16 mm diameter
1)
Hot dipped or electroplated minimum thickness coating of 1 µm.
2)
The coating should be smooth, continuous and free from flux stains with a minimum thickness coating of 50 µm.
3)
Applicable for air-termination rods only. For applications where mechanical stress such as wind loading is not
critical, a 10 mm diameter, 1 m long maximum air-termination rod with an additional fixing may be used.
4)
Applicable to earth lead-in rods only.
5)
Chromium ≥ 16 %, nickel ≥ 8 %, carbon ≤ 0,07 %.
6)
For stainless steel embedded in concrete, and/or in direct contact with flammable material, the minimum sizes
should be increased to 78 mm 2 (10 mm diameter) for solid round and 75 mm 2 (3 mm minimum thickness) for solid
tape.
7)
50 mm 2 (8 mm diameter) may be reduced to 28 mm 2 (6 mm diameter) in certain applications where mechanical
strength is not an essential requirement. Consideration should, in this case, be given to reducing the spacing of
the fasteners.
8)
If thermal and mechanical considerations are important, these dimensions can be increased to 60 mm 2 for solid
tape and to 78 mm 2 for solid round.
9)
The minimum cross-section to avoid melting is 16 mm 2 (copper), 25 mm 2 (aluminium), 50 mm 2 (steel) and 50 mm 2
(stainless steel) for a specific energy of 10 000 kJ/Ω. For further information see Annex E.
10) Thickness, width and diameter are defined at ±10 %.
62305-3 © IEC:2006
– 55 –
Table 7 – Material, configuration and minimum dimensions of earth electrodes
Minimum dimensions
Material
Copper
Configuration
Stranded
Earth rod
∅ mm
3)
Solid round
Solid tape
3)
3)
Solid round
15
Pipe
Steel
Earth conductor
Earth plate
mm
Comments
50 mm 2
1,7 mm min. diameter of
each strand
50 mm 2
8 mm diameter
50 mm 2
2 mm min. thickness
8)
20
2 mm min. wall thickness
Solid plate
500 x 500
2 mm min. thickness
Lattice plate
600 x 600
25 mm x 2 mm section
Minimum length of lattice
configuration: 4,8 m
Galvanized solid round
Galvanized pipe
1) 2)
16
1) 2)
9)
10 mm diameter
2 mm min. wall thickness
25
Galvanized solid tape
Galvanized solid plate
1)
90 mm 2
1)
Galvanized lattice plate
1)
Copper coated solid round
4)
14
3 mm min. thickness
500 x 500
3 mm min. thickness
600 x 600
30 mm x 3 mm section
250 µm minimum radial
Copper coating 99,9 %
copper content
Bare solid round
5)
10 mm diameter
Bare or galvanized solid
tape 5) 6)
Galvanized stranded
5) 6)
Galvanized cross profile
Stainless
steel 7)
1)
1)
Solid round
75 mm 2
3 mm min. thickness
70 mm 2
1,7 mm min. diameter of
each strand
50 x 50 x 3
15
Solid tape
10 mm diameter
100 mm 2
2 mm min. thick
The coating shall be smooth, continuous and free from flux stains with a minimum thickness of 50 µm for round
and 70 µm for flat material.
2)
Threads shall be machined prior to galvanizing.
3)
May also be tin-plated.
4)
The copper should be intrinsically bonded to the steel.
5)
Only allowed when completely embedded in concrete.
6)
Only allowed when correctly connected together at least every 5 m with the natural reinforcement steel of the
earth touching part of the foundation.
7)
Chromium ≥ 16 %, nickel ≥ 5 %, molybdenum ≥ 2 %, carbon ≤ 0,08 %.
8)
In some countries 12 mm is allowed.
9)
Earth lead in rods are used in some countries to connect the down-conductor to the point where it enters the
ground.
62305-3 © IEC:2006
6
– 57 –
Internal lightning protection system
6.1
General
The internal LPS shall avoid the occurrence of dangerous sparking within the structure to be
protected due to lightning current flowing in the external LPS or in other conductive parts of
the structure.
Dangerous sparking may occur between the external LPS and other components such as:
–
the metal installations;
–
the internal systems;
–
the external conductive parts and lines connected to the structure.
NOTE 1 Sparking occurring within the structure with danger of explosion is always dangerous. In this case
additional protective measures are required which are under consideration (see Annex E).
NOTE 2
For protection against overvoltages of internal systems, refer to IEC 62305-4.
Dangerous sparking between different parts can be avoided by means of
–
equipotential bonding in accordance with 6.2, or
–
electrical insulation between the parts in accordance with 6.3.
6.2
Lightning equipotential bonding
6.2.1
General
Equipotentialization is achieved by interconnecting the LPS with
–
structural metal parts,
–
metal installations,
–
internal systems,
–
external conductive parts and lines connected to the structure.
When lightning equipotential bonding is established to internal systems, part of the lightning
current may flow into such systems and this effect shall be taken into account.
Interconnecting means can be
–
bonding conductors, where the electrical continuity is not provided by natural bonding,
–
surge protective devices (SPDs), where direct connections with bonding conductors is not
feasible.
The manner in which lightning equipotential bonding is achieved is important and shall be
discussed with the operator of the telecommunication network, the electric power operator,
and other operators or authorities concerned, as there may be conflicting requirements.
SPDs shall be installed in such a way that they can be inspected.
NOTE When an LPS is installed, metalwork external to the structure to be protected may be affected. This should
be considered when designing such systems. Lightning equipotential bonding for external metalwork may also be
necessary.
62305-3 © IEC:2006
6.2.2
– 59 –
Lightning equipotential bonding for metal installations
In the case of an isolated external LPS, lightning equipotential bonding shall be established at
ground level only.
For an external LPS which is not isolated, lightning equipotential bonding shall be installed at
the following locations:
a) in the basement or approximately at ground level. Bonding conductors shall be connected
to a bonding bar constructed and installed in such a way that it allows easy access for
inspection. The bonding bar shall be connected to the earth-termination system. For large
structures (typically more than 20 m in length), more than one bonding bar can be
installed, provided that they are interconnected;
b) where insulation requirements are not fulfilled (see 6.3).
Lightning equipotential bonding connections shall be made as direct and straight as possible.
NOTE When lightning equipotential bonding is established to conducting parts of the structure, part of the
lightning current may flow into the structure and this effect should be taken into account.
The minimum values of the cross-section of the bonding conductors connecting different
bonding bars and of the conductors connecting the bars to the earth-termination system are
listed in Table 8.
The minimum values of the cross-section of the bonding conductors connecting internal metal
installations to the bonding bars are listed in Table 9.
Table 8 – Minimum dimensions of conductors connecting different bonding bars
or connecting bonding bars to the earth-termination system
Class of LPS
I to IV
Material
Cross-section
mm 2
Copper
14
Aluminium
22
Steel
50
Table 9 – Minimum dimensions of conductors connecting internal metal installations
to the bonding bar
Class of LPS
I to IV
Material
Cross-section
mm 2
Copper
5
Aluminium
8
Steel
16
If insulating pieces are inserted into gas lines or water pipes, inside the structure to be
protected they shall, with the agreement of the water and gas supplier, be bridged by SPDs
designed for such an operation.
SPDs shall have the following characteristics:
–
class I test;
–
I imp ≥ k c I
with k c I being the lightning current flowing along the relevant part of the
external LPS (see Annex C);
62305-3 © IEC:2006
– 61 –
–
the protection level U P shall be lower than the impulse withstand level of insulation
between parts;
–
other characteristics conforming to IEC 61643-12.
6.2.3
Lightning equipotential bonding for external conductive parts
For external conductive parts, lightning equipotential bonding shall be established as near as
possible to the point of entry into the structure to be protected.
Bonding conductors shall be capable of withstanding the part I f of the lightning current flowing
through them evaluated in accordance with Annex E of IEC 62305-1.
If direct bonding is not acceptable, SPDs with the following characteristics shall be used:
–
class I test;
–
I imp ≥ I f with I f being the lightning current flowing along the considered external conductive
part (see Annex E of IEC 62305-1);
–
the protection level U P shall be lower than the impulse withstand level of insulation
between parts;
–
other characteristics conforming to IEC 61643-12.
NOTE When equipotential bonding is required, but an LPS is not required, the earth-termination of the low voltage
electrical installation can be used for this purpose. IEC 62305-2 provides information on the conditions where an
LPS is not required.
6.2.4
Lightning equipotential bonding for internal systems
It is imperative that lightning equipotential bonding is installed in accordance with 6.2.2 a) and
6.2.2 b).
If the internal systems conductors are screened or located in metal conduits, it may be
sufficient to bond only these screens and conduits (see Annex B).
NOTE Bonding of screens and conduits may not avoid failure due to overvoltages of equipment connected to the
conductors. For protection of such equipment refer to IEC 62305-4.
If conductors of internal systems are neither screened nor located in metal conduits, they
shall be bonded via SPDs. In TN systems, PE and PEN conductors shall be bonded to the
LPS directly or with a SPD.
Bonding conductors and SPDs shall have the same characteristics as indicated in 6.2.2.
If protection of internal systems against surges is required, a “coordinated SPD protection”
conforming to the requirements of IEC 62305-4, Clause 7 shall be used.
6.2.5
Lightning equipotential bonding for lines connected to the structure to be
protected
Lightning equipotential bonding for electrical and telecommunication lines shall be installed in
accordance with 6.2.3.
All the conductors of each line should be bonded directly or with an SPD. Live conductors
shall only be bonded to the bonding bar via an SPD. In TN systems, PE or PEN conductors
shall be bonded directly or via SPD to the bonding bar.
62305-3 © IEC:2006
– 63 –
If lines are screened or routed into metal conduits, these screens and conduits shall be
bonded; lightning equipotential bonding for conductors is not necessary provided that the
cross-section S c of these screens or conduits is not lower than the minimum value S cmin
evaluated in accordance with Annex B.
Lightning equipotential bonding of the cable screens or of the conduits shall be performed
near the point where they enter the structure.
Bonding conductors and SPDs shall have the same characteristics as indicated in 6.2.3.
If protection against surges of internal systems connected to lines entering the structure is
required, a “coordinated SPD protection” conforming to the requirements of IEC 62305-4,
Clause 7 shall be used.
NOTE 1 When equipotential bonding is required, but an LPS is not required, the earth-termination of the low
voltage electrical installation can be used for this purpose. IEC 62305-2 provides information on the conditions
where an LPS is not required.
NOTE 2
6.3
For more information concerning equipotential bonding for telecommunication lines, see also IEC 62305-5.
Electrical insulation of the external LPS
The electrical insulation between the air-termination or the down-conductor and the structural
metal parts, the metal installations and the internal systems can be achieved by providing a
distance d between the parts greater than the separation distance s:
k
s = ki c l
km
(4)
where
ki
depends on the selected class of LPS (see Table 10);
kc
depends on the lightning current flowing on the down-conductors (see Table 11);
km
depends on the electrical insulation material (see Table 12);
l
is the length, in metres, along the air-termination or the down-conductor, from the point
where the separation distance is to be considered, to the nearest equipotential bonding
point.
Table 10 – Isolation of external LPS – Values of coefficient k i
Class of LPS
ki
I
0,08
II
0,06
III and IV
0,04
Table 11 – Isolation of external LPS – Values of coefficient k c
Number of down-conductors
n
Detailed values
(see Table C.1)
kc
1
1
2
1 … 0,5
4 and more
1 … 1/n
62305-3 © IEC:2006
– 65 –
Table 12 – Isolation of external LPS – Values of coefficient k m
Material
km
Air
1
Concrete, bricks
0,5
NOTE 1
When there are several insulating materials in series, it is good practice to use the lower value for k m .
NOTE 2
The use of other insulating materials is under consideration.
In the case of the lines or external conductive parts connected to the structure, it is always
necessary to ensure lightning equipotential bonding (by direct connection or connection by
SPD) at their point of entry in the structure.
In structures with metallic or electrically continuous, connected, reinforced, concrete
framework of the structures, a separation distance is not required.
7
7.1
Maintenance and inspection of an LPS
Application of inspections
The objective of the inspections is to ascertain that
a) the LPS conforms to the design based on this standard,
b) all components of the LPS are in good condition and capable of performing their designed
functions, and that there is no corrosion,
c) any recently added services or constructions are incorporated into the LPS.
7.2
Order of inspections
Inspections should be made according to 7.1 as follows:
–
during the construction of the structure, in order to check the embedded electrodes;
–
after the installation of the LPS;
–
periodically at such intervals as determined with regard to the nature of the structure to
be protected, i.e. corrosion problems and the class of LPS;
NOTE
–
For detailed information see Clause E.7.
after alterations or repairs, or when it is known that the structure has been struck by
lightning.
During the periodic inspection, it is particularly important to check the following:
–
deterioration and corrosion of air-termination elements, conductors and connections;
–
corrosion of earth electrodes;
–
earthing resistance value for the earth-termination system;
–
condition of connections, equipotential bonding and fixings.
7.3
Maintenance
Regular inspections are among the fundamental conditions for reliable maintenance of an
LPS. The property owner shall be informed of all observed faults and they shall be repaired
without delay.
62305-3 © IEC:2006
8
8.1
– 67 –
Protection measures against injury to living beings due to touch and step
voltages
Protection measures against touch voltages
In certain conditions, the vicinity of the down-conductors of an LPS, outside the structure,
may be hazardous to life even if the LPS has been designed and constructed according to the
above-mentioned requirements.
The hazard is reduced to a tolerable level if one of the following conditions is fulfilled:
a) the probability of persons approaching, or the duration of their presence outside the
structure and close to the down-conductors, is very low;
b) the natural down-conductor system consists of several columns of the extensive metal
framework of the structure or of several pillars of interconnected steel of the structure,
with the electrical continuity assured;
c) the resistivity of the surface layer of the soil, within 3 m of the down-conductor, is not less
than 5 kΩm.
NOTE A layer of insulating material, e.g. asphalt, of 5 cm thickness (or a layer of gravel 15 cm thick)
generally reduces the hazard to a tolerable level.
If none of these conditions are fulfilled, protection measures shall be adopted against injury to
living beings due to touch voltages as follows:
−
insulation of the exposed down-conductor is provided giving a 100 kV, 1,2/50 µs impulse
withstand voltage, e.g. at least 3 mm cross-linked polyethylene;
−
physical restrictions and/or warning notices to minimize the probability of down-conductors
being touched.
Protection measures shall conform to the relevant standards (see ISO 3864-1).
8.2
Protection measures against step voltages
In certain conditions, the vicinity of the down-conductors outside the structure may be
hazardous to life even if the LPS has been designed and constructed according to the abovementioned rules.
The hazard is reduced to a tolerable level if one of the following conditions is fulfilled:
a) the probability of persons approaching, or the duration of their presence in the dangerous
area within 3 m from the down-conductors, is very low;
b) the resistivity of the surface layer of the soil, within 3 m of the down-conductor, is not less
than 5 kΩm.
NOTE 1 A layer of insulating material, e.g. asphalt, of 5 cm thickness (or a layer of gravel 15 cm thick) generally
reduces the hazard to a tolerable level.
If none of these conditions is fulfilled, protection measures shall be adopted against injury to
living beings due to step voltages as follows:
−
equipotentialization by means of a meshed earthing system;
−
physical restrictions and/or warning notices to minimize the probability of access to the
dangerous area, within 3 m of the down-conductor.
Protection measures shall conform to the relevant standards (see ISO 3864-1).
62305-3 © IEC:2006
– 69 –
Annex A
(normative)
Positioning the air-termination system
A.1
Positioning the air-termination system when utilizing the protective angle
method
The position of the air-termination system is considered to be adequate if the structure to be
protected is fully situated within the protected volume provided by the air-termination system.
For the determination of the volume protected only the real physical dimensions of the metal
air-termination systems shall be considered.
A.1.1
Volume protected by a vertical rod air-termination system
The volume protected by a vertical rod is assumed to have the shape of a right circular cone
with the vertex placed on the air-termination axis, semi-apex angle α , depending on the class
of LPS, and on the height of the air-termination system as given in Table 2. Examples of the
protected volume are given in Figures A.1 and A.2.
A
α
h1
O
B
C
IEC 2098/05
Key
A
tip of an air-termination rod
B
reference plane
OC radius of protected area
h 1 height of an air-termination rod above the reference plane of the area to be protected
α
protective angle according to Table 2
Figure A.1 – Volume protected by a vertical air-termination rod
62305-3 © IEC:2006
– 71 –
α2
α1
h1
h1
h2
H
IEC 2099/05
Key
h 1 physical height of an air-termination rod
NOTE The protective angle α 1 corresponds to the air-termination height h 1 , being the height above the roof surface
to be protected; the protective angle α 2 corresponds to the height h 2 = h 1 + H, the ground being the reference
plane; α 1 is related to h 1 and α 2 is related to h 2 .
Figure A.2 – Volume protected by a vertical air-termination rod
A.1.2
Volume protected by a wire air-termination system
The volume protected by a wire is defined by the composition of the volume protected by
virtual vertical rods having vertexes on the wire. Examples of the protected volume are given
in Figure A.3.
A
α
h1
A
0
α
C
B
h1
0
C
IEC 2100/05
NOTE
See Figure A.1 for key.
Figure A.3 – Volume protected by a wire air-termination system
62305-3 © IEC:2006
A.1.3
– 73 –
Volume protected by wires combined in a mesh
The volume protected by wires combined in a mesh is defined by a combination of the
protected volume determined by the single conductors forming the mesh.
Examples of the volume protected by wires combined in a mesh is given in Figures A.4 and
A.5.
r
α1
α2
h1
h2
H
r = h2 tan α2
Air-termination
IEC 2101/05
Figure A.4 – Volume protected by isolated wires combined in a mesh according to the
protective angle method and rolling sphere method
62305-3 © IEC:2006
– 75 –
α
H
r′ = h tan α
IEC 2102/05
NOTE H = h.
Figure A.5 – Volume protected by non-isolated wires combined in a mesh according to
the mesh method and the protective angle method
A.2
Positioning of the air-termination system utilizing the rolling sphere
method
Applying this method, the positioning of the air-termination system is adequate if no point of
the structure to be protected comes into contact with a sphere with radius, r , depending on
the class of LPS (see Table 2), rolling around and on top of the structure in all possible
directions. In this way, the sphere only touches the air-termination system (see Figure A.6).
62305-3 © IEC:2006
– 77 –
r
r
r
r
r
h < 60 m
0,8 h
h > 60 m
Air termination system
r
Radius of rolling sphere
IEC 2103/05
NOTE 1
The rolling sphere radius r should comply with the selected class of LPS (see Table 2).
NOTE 2 H = h.
Figure A.6 – Design of an air-termination system according to the rolling sphere method
On all structures higher than the rolling sphere radius r , flashes to the side of structure may
occur. Each lateral point of the structure touched by the rolling sphere is a possible point of
strike. However, the probability for flashes to the sides is generally negligible for structures
lower than 60 m.
For taller structures, the major part of all flashes will hit the top, horizontal leading edges and
corners of the structure. Only a few per cent of all flashes will be to the side of the structure.
Moreover, observation data show that the probability of flashes to the sides decreases rapidly
as the height of the point of strike on tall structures when measured from the ground.
Therefore consideration should be given to install a lateral air-termination system on the
upper part of tall structures (typically the top 20 % of the height of the structure). In this case
the rolling sphere method will be applied only to the positioning of the air-termination system
of the upper part of the structure.
A.3
Positioning of the air-termination system utilizing the mesh method
For the purposes of protecting flat surfaces, a mesh is considered to protect the whole
surface, dependent upon all of the following conditions being fulfilled:
a) Air-termination conductors are positioned
–
on roof edge lines,
–
on roof overhangs,
–
on roof ridge lines, if the slope of the roof exceeds 1/10.
62305-3 © IEC:2006
– 79 –
NOTE 1
The mesh method is suitable for horizontal and inclined roofs with no curvature.
NOTE 2
The mesh method is suitable for flat lateral surfaces to protect against side flashes.
NOTE 3 If the slope of the roof exceeds 1/10, parallel air-termination conductors, instead of a mesh, may be
used provided the distance between the wires is not greater than the required mesh width.
b) The mesh dimensions of the air-termination network are not greater than the values given
in Table 2.
c) The network of the air-termination system is constructed in such a way that the lightning
current will always encounter at least two distinct metal routes to earth termination.
d) No metal installation protrudes outside the volume protected by air-termination systems.
NOTE 4
Further information can be found in Annex E.
e) The air-termination conductors follow, as far as possible, the shortest and most direct
route.
62305-3 © IEC:2006
– 81 –
Annex B
(normative)
Minimum cross-section of the entering cable screen
in order to avoid dangerous sparking
The overvoltages between the active conductors and the screen of a cable may cause
dangerous sparking due to the lightning current carried by the screen. The overvoltages
depend on the material, the dimensions of the screen, and the length and positioning of the
cable.
The minimum value S cmin (in mm 2 ) of the cross-sectional area of the screen to avoid
dangerous sparking is given by:
Sc min =
I f × ρc × Lc × 10 6
Uw
(mm 2 )
(B.1)
where
If
is the current flowing on the screen, in kA;
ρc is the resistivity of the screen, in Ωm;
L c is the cable length, in m (see Table B.1);
U w is the impulse withstand voltage of the electrical/electronic system fed by the cable, in kV.
Table B.1 – Cable length to be considered according to the condition of the screen
Condition of the screen
Lc
In contact with a soil with resistivity ρ (Ωm)
L c ≤ 8 × √ρ
Insulated from the soil or in air
L c distance between the structure and the closest
earthing point of the screen
NOTE It should be ascertained whether an unacceptable temperature rise for the insulation of the line could occur
when the lightning current flows along the line shield or the line conductors. For detailed information, see
IEC 62305-4.
The limits of the current are given:
– for shielded cables, by I f = 8 × S c ; and
– for unshielded cables, by I f = 8 × n′ × S′ c
where
If
is the current on the screen, in kA;
n′ is the number of conductors;
S c is the cross-section of the screen, in mm 2 ;
S′ c is the cross-section of each conductor, in mm 2 .
62305-3 © IEC:2006
– 83 –
Annex C
(informative)
Partitioning of the lightning current amongst down-conductors
The partitioning coefficient k c of the lightning current amongst the down-conductors depends
on the overall number of down-conductors n and their position, the interconnecting ring
conductors, the type of air-termination system and the type of earth-termination system as
indicated in Table C.1.
Table C.1 applies for type A earthing arrangements, provided that the earthing resistance of
each electrode has a similar value, and for all type B earthing arrangements.
Table C.1 – Values of coefficient k c
Type
of air-termination system
Number of downconductors
n
Single rod
1
kc
Earthing arrangement
type A
1
Earthing arrangement
type B
1
Wire
2
0,66
d)
Mesh
4 and more
0,44
d)
0,25... 0,5 (see Figure C.2)
Mesh
4 and more, connected by
horizontal ring conductors
0,44
d)
1/n... 0,5 (see Figure C.3)
0,5... 1 (see Figure C.1)
a)
b)
c)
a)
Values range from k c = 0,5 where c << h to k c = 1 with h << c (see Figure C.1).
b)
The equation for k c according to Figure C.2 is an approximation for cubic structures and for n ≥ 4. The values of
h, c s and c d are assumed to be in the range of 5 m to 20 m.
c)
If the down-conductors are connected horizontally by ring conductors, the current distribution is more
homogeneous in the lower parts of the down-conductor system and k c is further reduced. This is especially valid
for tall structures.
d)
These values are valid for single earthing electrodes with comparable earthing resistances. If earthing
resistances of single earthing electrodes are clearly different, k c = 1 is to be assumed
NOTE
Other values of k c may be used if detailed calculations are performed.
62305-3 © IEC:2006
– 85 –
c
H
IEC 2104/05
kc =
h+c
2h + c
NOTE H = h.
Figure C.1 – Values of coefficient k c in the case of a wire air-termination system and a
type B earth-termination system
62305-3 © IEC:2006
– 87 –
c
h
IEC 2105/05
kc =
1
c
+ 0,1 + 0,2 × 3
2n
h
Key
n
total number of down-conductors
c
distance of a down-conductor to the next down-conductor
h
spacing (or height) between ring conductors
NOTE 1
For a detailed evaluation of coefficient k c values, see Figure C.3.
NOTE 2
If internal down-conductors exist, they should be taken into account in evaluating k c .
Figure C.2 – Values of coefficient k c in the case of a mesh air-termination system
and type B earth-termination system
62305-3 © IEC:2006
– 89 –
d a ≥ sa =
ki
× k c1 × la
km
d b ≥ sb =
ki
× k c2 × lb
km
d c ≥ sc =
ki
× k c3 × lc
km
d e ≥ se =
ki
× k c4 × le
km
d f ≥ sf =
ki
× ( k c1 × l f + k c2 × h2 )
km
d g ≥ sg =
ki
× (kc2 × lg + kc3 × h3 + kc4 × h4 )
km
d a ≥ sa =
ki
× k c1 × la
km
d b ≥ sb =
ki
× k c2 × lb
km
d c ≥ sc =
ki
× k c3 × lc
km
d e ≥ se =
ki
× k c4 × le
km
d f ≥ sf =
ki
× ( k c1 × l f + k c2 × h2 )
km
d g ≥ sg =
ki
× (kc2 × lg + kc3 × h3 + kc4 × h4 )
km
c
h1
la
kc =
df
c
da
1
c
+ 0,1 + 0,2 × 3
2n
h
lf
k c2 =
1
+ 0,1
n
k c3 =
1
+ 0,01
n
h2
lb
db
dg
lg
h3
lc
k c4 =
dc
1
n
k cm = k c 4 =
h4
le
1
n
de
Key
n
c
h
m
d
l
hm
IEC
Total number of down-conductors
Distance from the nearest down-conductor
Spacing (height) between ring conductors
Total number of levels
Distance to the nearest down-conductor
Height above the bonding point
2106/05
Figure C.3 – Examples of calculation of the separation distance in the case of a meshed
air-termination system, an interconnecting ring of the down-conductors at each level
and a type B earth-termination system
62305-3 © IEC:2006
– 91 –
Annex D
(informative)
Additional information for LPS in the case of structures
with a risk of explosion
D.1
General
This annex supplies additional information for the design, construction, extension and
modification of lightning protection systems for structures with a risk of explosion.
NOTE 1 Information provided in this annex is based on practically proven configurations of lightning protection
systems installed in applications where a danger of explosion exists.
Where protection against lightning is required by the authority having jurisdiction, or as result
of risk assessment performed in accordance with IEC 62305-2, at least a class II LPS should
be adopted. Supplemental information is provided in this annex for specific applications.
NOTE 2 Exceptions to the use of lightning protection level II may be allowed when technically justified and
authorized by the authority having jurisdiction. For example, the use of lightning protection level I is allowed in all
cases, especially in those cases where the environments or contents within the structure are exceptionally
sensitive to the effects of lightning. In addition, authorities having jurisdiction may choose to allow lightning
protection level III systems where the infrequency of lightning activity and/or the insensitivity of the contents of the
structure warrants such.
D.2
Additional terms and definitions
In addition to the terms and definitions of Clause 3 of this standard, the following terms and
definitions are applicable to this annex.
D.2.1
isolating spark gap
component with discharge distance for isolating electrically-conductive installation sections
NOTE In the event of a lightning flash, the installation sections are temporarily connected conductively as the
result of the discharge.
D.2.2
solid explosives material
solid chemical compound, mixture, or device with explosion as its primary or common purpose
D.2.3
zone 0
place in which an explosive atmosphere consisting of a mixture of air and flammable
substances in the form of gas, vapour or mist is present continuously or for long periods or
frequently
[IEV 426-03-03, modified]
D.2.4
zone 1
place in which an explosive atmosphere consisting of a mixture of air and flammable
substances in the form of gas, vapour or mist is likely to occur in normal operation
occasionally
[IEV 426-03-04, modified]
62305-3 © IEC:2006
– 93 –
D.2.5
zone 2
place in which an explosive atmosphere consisting of a mixture of air and flammable
substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it
does occur, will persist for a short period only
[IEV 426-03-05, modified]
NOTE 1 In this definition, the word "persist" means the total time for which the flammable atmosphere will exist.
This will normally comprise the total of the duration of the release, plus the time taken for the flammable
atmosphere to disperse after the release has stopped.
NOTE 2 Indications of the frequency of the occurrence and duration may be taken from codes relating to specific
industries or applications.
D.2.6
zone 20
place in which an explosive atmosphere, in the form of a cloud of combustible dust in air, is
present continuously, or for long periods, or frequently
[IEC 61241-10:1997, modified]
D.2.7
zone 21
place in which an explosive atmosphere in the form of a cloud of combustible dust in air, is
likely to occur in normal operation occasionally
[IEC 61241-10:1997, modified]
D.2.8
zone 22
place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not
likely to occur in normal operation but, if it does occur, will persist for a short period only
[IEC 61241-10:1997]
D.3
D.3.1
Basic requirements
General
The lightning protection system should be designed and installed in such a manner that, in
case of a direct lightning flash, there are no melting or spraying effects except at the striking
point.
NOTE Sparks or damaging impact at the striking point may also be experienced. This should be taken into
consideration in the determination of air-termination device locations. Down-conductors should be installed in such
a way that the auto-ignition temperature given by the source of the relative hazardous area will not be exceeded in
those applications where it is not possible to install down-conductors outside of the hazardous area.
D.3.2
Required information
The lightning protection system installer/designer should be provided with drawings of the
plant(s) to be protected, with the areas in which solid explosives material will be handled or
stored and hazardous areas according to IEC 60079-10 and IEC 61241-10 appropriately
marked.
62305-3 © IEC:2006
D.3.3
– 95 –
Earthing
A type B arrangement for the earth-termination system, according to 5.4.2.2, is preferred for
all lightning protection systems for structures with danger of explosion.
NOTE The construction of a structure may provide the effective equivalent of the ring conductor of type B
arrangement (for example metallic storage tanks).
The earthing resistance of earth-termination systems for structures containing solid
explosives materials and explosive mixtures should be as low as possible but not greater than
10 Ω.
D.3.4
Equipotential bonding
Lightning equipotential bonding between LPS components and other conductive installations,
as well as between the components of all conductive installations, according to 6.2, should be
assured inside hazardous areas and locations where solid explosive material may be present:
–
at ground level;
–
where the distance between the conductive parts is less than the separation distance s
calculated assuming k c = 1.
NOTE Because of dangerous partial discharges, the separation distances may only be considered in the areas
without explosive mixtures. In those areas where a spark may cause ignition of the environment, additional
equipotential bonding will be necessary in order to ensure no internal sparking in zone 0 and zone 20 hazardous
areas.
D.4
Structures containing solid explosives material
The design of lightning protection for structures containing solid explosive material should
take into consideration the sensitivity of the material in the configuration in which it is used or
stored. For instance, some insensitive bulk explosive material may not require any additional
consideration other than those contained within this annex. However, there are some
configurations of sensitive explosive materials that may be sensitive to rapidly changing
electrical fields and/or radiated by lightning impulsive electromagnetic field. It may be
necessary to establish additional bonding or shielding requirements for such applications.
For structures containing solid explosive materials, an isolated external LPS (as defined in
5.1.2) is encouraged. Structures totally contained within a metallic shell of 5 mm thickness
steel or equivalent (7 mm for aluminium structures) may be considered protected by a natural
air-termination system as defined by 5.2.5. The earthing requirements of 5.4 are applicable
for such structures.
Surge protective devices (SPDs) should be provided as part of the LPS for all locations where
explosive material is present. Where practicable, SPDs should be positioned outside locations
where solid explosive material is present. SPDs positioned inside locations where exposed
explosives or explosive dust is present should be of explosion-proof type or contained within
explosion-proof enclosures.
D.5
D.5.1
Structures containing hazardous areas
General
All parts of the external LPS (air-termination and down-conductors) should be at least 1 m
away from a hazardous zone, where possible. Where this is not possible, conductors passing
within 0,5 m of a hazardous zone should be continuous or connections should be made with
compression fittings or by welding.
62305-3 © IEC:2006
– 97 –
Where a hazardous area is located directly under a metal sheet that may be punctured by
lightning (see 5.2.5) air-termination shall be provided in accordance with the requirements of 5.2.
D.5.1.1
Surge suppression
Surge protective devices should be positioned outside the hazardous zone where practicable.
Surge protective devices positioned inside the hazardous zone should be approved for the
hazardous zone in which they are installed or should be contained within an enclosure and
the enclosures including surge suppression shall be approved for this service.
D.5.1.2
Equipotential bonding
In addition to the bonding requirements of D.3.4, common equipotential bonding should be
provided for the lightning protection system in accordance with the normative requirements of
this standard, IEC 60079-14, and IEC 61241-14.
Connections to piping should be of such a kind that, in the instance of a lightning current
passage, there is no sparking. Suitable connections to piping are welded on lugs or bolts or
tap holes in the flanges for taking up screws. Connections by means of clips are only allowed
if, in the instance of lightning currents, ignition protection is proved by tests and procedures
are utilized to ensure the reliability of the connection. Junctions should be provided for the
joining of connection and earthing leads to containers and tanks.
D.5.2
Structures containing zones 2 and 22
Structures where areas defined as zones 2 and 22 exist may not require supplemental
protection measures.
For production facilities made of metal (e.g. outdoor columns, reactors, containers with areas
containing zones 2 and 22) of thickness and material meeting the requirements of Table 3,
the following applies:
–
air-termination devices and down-conductors are not required;
–
production facilities should be earthed according to Clause 5.
D.5.3
Structures containing zones 1 and 21
For structures where areas defined as zones 1 and 21 exist, the requirements for zones 2 and
22 apply with the following additions:
–
if there are insulation pieces in pipelines, the operator should determine the protective
measures. For instance, a disruptive discharge can be avoided by the use of explosionprotected, isolating spark gaps;
–
the isolating spark gaps and the insulation pieces should be inserted outside the
explosion-endangered areas.
D.5.4
Structures containing zones 0 and 20
For structures where areas defined as zones 0 and 20 exist, the requirements of D.5.3 apply,
supplemented by the recommendations given in this clause as applicable.
Lightning equipotential bonding connections between the lightning protection system and
other installations/structures/equipment will be carried out with the agreement of the system
operator. Lightning equipotential bonding connections utilizing spark gaps may not be made
without the agreement of the system operator. Such devices shall be suitable for the
environment in which they are installed.
For outdoor facilities with areas defined as zones 0 and 20, the requirements for zones 1, 2,
21 and 22 apply with the following additions:
62305-3 © IEC:2006
– 99 –
–
 e lectrical equipment inside tanks containing flammable liquids should be suitable for this
use. Measures for lightning protection should be taken according to the type of
construction;
–
closed steel containers with areas defined as zones 0 and 20 inside should have a wall
thickness of at least 5 mm at the possible lightning striking points. In the case of thinner
walls, air-termination devices should be installed.
D.5.5
Specific applications
D.5.5.1
Filling stations
At filling stations for cars, railways, ships etc., with hazardous areas defined as zones 2 and
22, the metal pipelines should be earthed according to Clause 5. Pipelines should be
connected with steel constructions and rails, where existing (if necessary via isolating spark
gaps approved for the hazardous zone in which it is installed), to take into account railway
currents, stray currents, electrical train fuses, cathodic-corrosion-protected systems and the
like. Decanting stations at electrical railways are subject to national standards.
D.5.5.2
Storage tanks
Certain types of structures used for the storage of liquids that can produce flammable vapours
or used to store flammable gases are essentially self-protecting (contained totally within
continuous metallic containers having a thickness of not less than 5 mm of steel or 7 mm of
aluminium, with no spark gaps) and require no additional protection. Similarly, soil-covered
tanks and pipelines do not require the installation of air-termination devices. Instrumentation
or electrics used inside this equipment should be approved for this service. Measures for
lightning protection should be taken according to the type of construction.
Isolated tanks or containers should be earthed according to Clause 5, depending on the
greatest horizontal dimension (diameter or length):
–
up to 20 m: once
–
over 20 m: twice.
For tanks in tank farms (for example refineries and tank stores), the earthing of every tank at
one point only is sufficient, independent of the greatest horizontal dimension. The tanks in
tank farms shall be connected with each other. Beside connections according to Tables 7 and
8, pipelines, which are connected so that they are electrically-conductive according to 5.3.5,
may also be used as connections.
NOTE
In some countries additional requirements may exist.
In the case of floating-roof tanks, the floating-roof should be effectively bonded to the main
tank shell. The design of the seals and shunts and their relative locations needs to be
carefully considered so that the risk of any ignition of a possible explosive mixture by
incendiary sparking is reduced to the lowest level practicable. When a rolling ladder is fitted, a
flexible bonding conductor of 35 mm width should be applied across the ladder hinges,
between the ladder and the top of the tank and between the ladder and the floating roof.
When a rolling ladder is not fitted to the floating-roof tank, one or more, (depending on the
size of the tank), flexible bonding conductors of 35 mm width, or equivalent, shall be applied
between the tank shell and the floating roof. The bonding conductors should either follow the
roof drain or be arranged so that they cannot form re-entrant loops. On floating roof tanks,
multiple shunt connections should be provided between the floating-roof and the tank shell at
about 1,5 m intervals around the roof periphery. Material selection is given by product and/or
environmental requirements. Alternative means of providing an adequate conductive
connection between the floating roof and tank shell for impulse currents associated with
lightning discharges are only allowed if proved by tests and if procedures are utilized to
ensure the reliability of the connection.
62305-3 © IEC:2006
D.5.5.3
– 101 –
Pipelines
Overground metal pipelines outside the production facilities should be connected every 30 m
to the earthing system, or should be earthed by a surface earthing electrode or an earthing
rod.
The following applies for long distance lines for the transport of flammable liquids.
−
in pumping sections, sliding sections and similar facilities, all lead-in piping including the
metal sheath pipes should be bridged by lines with a cross-section of at least 50 mm 2 ;
−
the bridging lines should be connected with specially welded-on lugs, or by screws which
are self-loosening, secure to the flanges of the lead-in pipes. Insulating pieces should be
bridged by spark gaps.
D.6
Inspection and maintenance
Recommendations on the inspection and maintenance of lightning protection systems are
provided in Clause E.7.
62305-3 © IEC:2006
– 103 –
Annex E
(informative)
Guidelines for the design, construction, maintenance
and inspection of lightning protection systems
E.1
General
This annex provides guidance on the physical design and construction, maintenance and
inspection of an LPS conforming to this standard.
This annex should be used and is only valid together with other parts of this standard.
Examples are given of protection techniques, which have the approval of international
experts.
NOTE The examples given in this annex illustrate one possible method of achieving protection. Other methods
may be equally valid.
E.2
Structure of this annex
In this annex the main clause numbers mirror the clause numbers of the main document. This
gives an easy reference between the two parts.
To achieve this goal, Clause E.3 is not used in this annex.
E.3
Vacant
E.4
Design of lightning protection systems (LPS)
E.4.1
General remarks
The construction of an LPS for an existing structure should always be weighed against other
measures of lightning protection conforming to this standard which give the same protection
level for reduced costs. For selection of the most suitable protection measures, IEC 62305-2
applies.
The LPS should be designed and installed by LPS designers and installers.
The designer and installer of an LPS should be capable of assessing both the electrical and
mechanical effects of the lightning discharge and be familiar with the general principles of
electromagnetic compatibility (EMC).
Furthermore, the lightning protection designer should be capable of assessing corrosion
effects and judging when it is necessary to seek expert assistance.
The lightning protection installer should be trained in the proper installation of the LPS
components in accordance with the requirements of this standard and the national rules
regulating construction work and the building of structures.
62305-3 © IEC:2006
– 105 –
The functions of an LPS designer and installer may be performed by the same person.
A thorough knowledge of the relevant standards and several years of experience is required
to become a specialized designer or installer.
Planning, implementation and testing of an LPS encompasses a number of technical fields
and makes demands for coordination by all parties involved with the structure to ensure the
achievement of the selected lightning protection level with minimum cost and lowest possible
effort. The management of the LPS should be efficient if the steps in Figure E.1 are followed.
Quality assurance measures are of great importance; in particular for structures including
extensive electrical and electronic installations.
62305-3 © IEC:2006
– 107 –
Characteristics of the structure to be
protected
Risk assessment and determination of
required protection level
Selection of type of external LPS
Type of materials
(corrosion problems)
(flammable surfaces)
Sizing of lightning
protection components
Natural
components
Air-termination system
Horizontal
roof-conductors
mesh system
Vertical
air-termination
rods
Overhead
air-termination
wires
Natural
terminations
Down-conductor system
Design of
down- conductors
Concealed or
exposed
Number
required
Natural
components
Earth-termination system
B type foundation
electrode
A or A and B type earth
electrodes
Natural
components
Internal LPS design
Bonding and
screening
Proximities and
cable routing
SPD
LPS design drawings and specifications
IEC
NOTE Interfaces z require the full cooperation of the architect, engineer and lightning protection designer.
Figure E.1 – LPS design flow diagram
2107/05
62305-3 © IEC:2006
– 109 –
The quality assurance measures extend from the planning stage, in which all drawings should
be approved, through the LPS construction stage during which all essential parts of the LPS
inaccessible for inspection after the construction works have been finished should be
checked. Quality assurance measurement continues through the acceptance stage, when final
measurements on the LPS should be performed together with the completion of the final test
documentation and finally through the entire lifetime of the LPS, by specifying careful periodic
inspections in accordance with the maintenance programme.
Where modifications are made to a structure or its installations, a check should be made to
determine whether the existing lightning protection still conforms to this standard. If it is found
that the protection is inadequate, improvements should be implemented without delay.
It is recommended that the materials, extent and dimensions of the air-termination system,
down-conductors, earth-termination system, bonding, components, etc. should conform to this
standard.
E.4.2
E.4.2.1
Design of the LPS
Planning procedure
Before any detailed design work on the LPS is commenced, the lightning protection designer
should, where reasonably practical, obtain basic information regarding the function, general
design, construction and location of the structure.
Where the LPS has not already been specified by the licensing authority, insurer or
purchaser, the lightning protection designer should determine whether or not to protect the
structure with an LPS by following the procedures for risk assessment given in IEC 62305-2.
E.4.2.2
E.4.2.2.1
Consultation
General information
In the design and construction stages of a new structure, the LPS designer, LPS installer and
all other persons responsible for installations in the structure or for regulations pertaining to
the use of the structure (e.g. purchaser, architect, builder) should be in consultation regularly.
The flow diagram given in Figure E.1 will facilitate the rational design of an LPS.
In the design and construction stages of an LPS for an existing structure, consultations should
be held as far as reasonably practical with the persons responsible for the structure, its use,
installations and incoming services.
The consultations may have to be arranged through the owner, the building contractor of the
structure or their appointed representative. For existing structures, the LPS designer should
provide drawings which should be modified by the LPS installer, where necessary.
Regular consultations between the involved parties should result in an effective LPS at the
lowest possible cost. For example, the coordination of LPS design work with construction
work will often do away with the need for some bonding conductors and reduce the length of
those which are necessary. Building costs are often reduced substantially by the provision of
common routes for various installations within a structure.
62305-3 © IEC:2006
– 111 –
Consultation is important throughout all stages of the construction of a structure as
modifications to the LPS may be required due to changes in the structure design.
Consultation is also necessary so that arrangements can be agreed to facilitate inspection of
the parts of the LPS which will become inaccessible for visual control after the structure is
completed. In these consultations, the location of all connections between natural
components and the LPS should be determined. Architects are normally available to arrange
and coordinate consultation meetings for new building projects.
E.4.2.2.2
The principal consulting parties
The lightning protection designer should hold relevant technical consultations with all parties
involved in the design and construction of the structure, including the owner of the structure.
Particular areas of responsibility for the total installation of the LPS should be defined by the
LPS designer in conjunction with the architect, electrical contractor, building contractor, the
LPS installer (LPS supplier) and, where relevant, a historical adviser and the owner or
owner’s representative.
The clarification of responsibility for the various parties involved in the management of the
design and construction of the LPS is of particular importance. An example might be where
the waterproofing of the structure is punctured by roof-mounted LPS components or by earth
electrode connection conductors made below the structure foundation.
E.4.2.2.2.1
Architect
Agreement should be reached with the architect on the following items:
a) routing of all LPS conductors;
b) materials for LPS components;
c) details of all metal pipes, gutters, rails and similar items;
d) details of any equipment, apparatus, plant installations, etc. to be installed on, within or
near the structure which may require the moving of installations or may require bonding to
the LPS because of the separation distance. Examples of installations are alarm systems,
security systems, internal telecommunication systems, signal and data processing
systems, radio and TV circuits;
e) the extent of any buried conductive service which could affect the positioning of the earthtermination network and be required to be placed at a safe distance from the LPS;
f)
the general area available for the earth-termination network;
g) the extent of the work and the division of responsibility for primary fixings of the LPS to
the structure. For example, those affecting the water tightness of the fabric (chiefly
roofing), etc;
h) conductive materials to be used in the structure, especially any continuous metal which
may have to be bonded to the LPS, for example stanchions, reinforcing steel and metal
services either entering, leaving, or within the structure;
i)
the visual impact of the LPS;
j)
the impact of the LPS on the fabric of the structure;
k) the location of the connection points to the reinforcing steel, especially where they
penetrate external conductive parts (pipes, cable shields, etc.);
l)
the connection the LPS to the LPS of adjacent buildings.
62305-3 © IEC:2006
E.4.2.2.2.2
– 113 –
Public utilities
Bonding of incoming services to the LPS directly or, if this is not possible, through spark gaps
or SPD should be discussed with the operator or authorities concerned, as there may be
conflicting requirements.
E.4.2.2.2.3
Fire and safety authorities
Agreement should be reached with the fire and safety authorities on the following items:
–
the positioning of alarm and fire extinguishing system components;
–
routes, construction material and sealing of ducts;
–
the method of protection to be used in the case of a structure with a flammable roof.
E.4.2.2.2.4
Electronic system and external antenna installers
Agreement with the electronic system and antenna installer should be reached on the
following items:
–
the isolating or bonding of aerial supports and conductive shields of cables to the LPS;
–
the routing of aerial cables and internal network;
–
installation of surge protective devices.
E.4.2.2.2.5
Builder and installer
Agreement on the following items should be reached between the builder, installer, and those
responsible for construction of the structure and its technical equipment:
a) the form, position and number of primary fixings of the LPS to be provided by the builder;
b) any fixings provided by the LPS designer (or the LPS contractor or the LPS supplier) to be
installed by the builder;
c) the position of LPS conductors to be placed beneath the structure;
d) whether any components of the LPS are to be used during the construction phase, for
example the permanent earth-termination network could be used for earthing cranes,
hoists and other metallic items during construction work on the site;
e) for steel-framed structures, the number and position of stanchions and the form of fixing to
be made for the connection of earth terminations and other components of the LPS;
f)
whether metal coverings, where used, are suitable as components of the LPS;
g) the method of ensuring the electrical continuity of the individual parts of the coverings and
their method of connecting them to the rest of the LPS where metal coverings are suitable
as components of the LPS;
h) the nature and location of services entering the structure above and below ground
including conveyor systems, television and radio aerials and their metal supports, metal
flues and window cleaning gear;
62305-3 © IEC:2006
– 115 –
i)
coordination of the structure's LPS earth-termination system with the bonding of power
and communication services;
j)
the position and number of flag masts, roof-level plant rooms, for example lift motor
rooms, ventilation, heating and air-conditioning plant rooms, water tanks and other salient
features;
k) the construction to be employed for roofs and walls in order to determine appropriate
methods of fixing LPS conductors, specifically with a view to maintaining the watertightness of the structure;
l)
the provision of holes through the structure to allow free passage of LPS downconductors;
m) the provision of bonding connections to steel frames, reinforcement bars and other
conductive parts of the structure;
n) the frequency of inspection of LPS components which will become inaccessible, for
example steel reinforcing bars encapsulated in concrete;
o) the most suitable choice of metal for the conductors taking account of corrosion,
especially at the point of contact between dissimilar metals;
p) accessibility of test joints, provision of protection by non-metallic casings against
mechanical damage or pilferage, lowering of flag masts or other movable objects, facilities
for periodic inspection especially for chimneys;
q) the preparation of drawings incorporating the above details and showing the positions of
all conductors and main components;
r)
the location of the connection points to the reinforcing steel.
E.4.2.3
E.4.2.3.1
Electrical and mechanical requirements
Electrical design
The LPS designer should select the appropriate LPS to obtain the most efficient construction.
This means consideration of the architectural design of the structure to determine whether an
isolated or non-isolated LPS, or a combination of both types of lightning protection, should be
used.
Soil resistivity tests should be performed preferably prior to finalizing the design of an LPS
and should take into consideration the seasonal variations of soil resistivity.
During the completion of the basic electrical design of the LPS, the use of suitable conductive
parts of the structure should be considered as natural components of the LPS to enhance or
act as essential components of the LPS.
It is the responsibility of the LPS designer to evaluate the electrical and physical properties of
natural components of the LPS and to ensure that they conform to the minimum requirements
of this standard.
The use of metal reinforcing, such as steel reinforced concrete, as lightning protection
conductors requires careful consideration, and knowledge of the national construction
standards applicable to the structure to be protected. The steel skeleton of reinforced
concrete may be used as LPS conductors or may be used as a conductive shielding layer to
reduce the electromagnetic fields generated by lightning in the structure as the lightning
currents are conducted through an isolated LPS. This LPS design makes protection easier, in
particular for special structures containing extensive electrical and electronic installations.
A stringent construction specification for down-conductors is required in order to meet the
minimum requirements for natural components given in 5.3.5.
62305-3 © IEC:2006
E.4.2.3.2
– 117 –
Mechanical design
The lightning protection designer should consult with the persons responsible for the structure
on mechanical design matters following the completion of the electrical design.
Aesthetic considerations are particularly important as well as the correct selection of materials
to limit the risk of corrosion.
The minimum size of lightning protection components for the various parts of the LPS are
listed in Tables 3, 6, 7, 8 and 9.
The materials used for the LPS components are listed in Table 5.
NOTE For selection of other components, such as rods and clamps, reference may be made to the EN 50164
series. This will ensure that temperature rise and mechanical strength of such components are taken into account.
Where deviations are made from the dimensions and materials specified in Tables 5, 6 and 7,
using the lightning discharge electrical parameters specified for the selected class of LPS
given in Table 1, the lightning protection designer or installer should predict the temperature
rise of lightning conductors under discharge conditions and dimension the conductors
accordingly.
When excessive temperature rise is a concern for the surface on which the components are to
be attached (because it is flammable or has a low melting point), either larger conductor
cross-sections should be specified or other safety precautions should be considered, such as
the use of stand-off fittings or the insertion of fire-resistant layers.
The LPS designer should identify all corrosion problem areas and specify appropriate
measures.
The corrosion effects on the LPS may be reduced either by increases in material size, by
using corrosion resistive components, or by taking other corrosion protection measures.
The LPS designer and LPS installer should specify conductor fasteners and fixtures which will
withstand the electrodynamic forces of lightning current in the conductors and also allow for
the expansion and contraction of conductors due to the increase in temperature that occurs.
E.4.2.4
E.4.2.4.1
Design calculation
Evaluation of the coefficient k c
The partitioning coefficient k c of the lightning current among the down-conductors depends on
the overall number n and on the position of the down-conductors, the interconnecting ring
conductors, the type of air-termination system and the type of earth-termination system (see
Table C.1 and Figures C.2 and C.3).
For the determination of k c on roofs when earthing arrangement type A is installed, Figure E.2
may be used.
The necessary separation distance depends on the voltage drop of the shortest path from the
point where the separation distance is to be considered, to the ground electrode or the
nearest equipotential bonding point.
62305-3 © IEC:2006
– 119 –
c
=
h
0,33
0,50
1,00
2,00
kc
0,57
0,60
0,66
0,75
h
c
c Distance from the
nearest down-conductor
along the ridge
kc
0,47
0,52
0,62
0,73
h Length of the down-conductor
from the ridge to the next
equipotentional bonding point
or to the earth-termination
system
The values of k c , shown in the
table, refer to the downconductors represented by a
thick line and a strike point
kc
0,44
0,50
0,62
0,73
The location of the down
conductor (to be considered
for k c ) is to be compared with
the figure representative for
that down-conductor
The actual relation c/h is to
be determined.
If this relation ranges between
two values in the columns,
k c may be found by interpolation
kc
0,40
0,43
0,50
0,60
kc
kc
0,35
0,39
0,47
0,59
NOTE 1
Additional down-conductors
With more distance than
illustrated in the figures are
of nsignificant influence.
NOTE 2
In case of interconnecting
ring-conductors below the ridge
see Figure C.3
NOTE 3
The values are determined by
simple calculation of parallel
impedances following the
formula of Figure C.1
kc
c
h
0,31
0,35
0,45
0,58
62305-3 © IEC:2006
– 121 –
c
=
h
0,33
0,50
1,00
2,00
kc
0,31
0,33
0,37
0,41
kc
0,28
0,33
0,37
0,41
h
c
c Distance from the
nearest down-conductor
along the ridge
h Length of the down-conductor
from the ridge to the next
equipotentional bonding point
or to the earth-termination
system
kc
0,27
0,33
0,37
0,41
The values of k c , shown in the
table, refer to the downconductors represented by a
thick line and a strike point
NOTE 1
Additional down-conductors
With more distance than
illustrated in the figures are
of nsignificant influence.
kc
0,23
0,25
0,30
0,35
NOTE 2
In case of interconnecting
ring-conductors below the ridge
see Figure C.3
kc
0,21
0,24
0,29
0,35
kc
0,20
0,23
0,29
0,35
NOTE 3
The values are determined by
simple calculation of parallel
impedances following the
formula of Figure C.1
h
c
Figure E.2 – Values of coefficient k c in case of a sloped roof with air-termination
on the ridge and a type B earthing system
IEC
2108/05
62305-3 © IEC:2006
– 123 –
If the conductor has the same current flowing down its total length, the formula for the
necessary separation distance in air is given by
s = ki × kc × l
(E.1)
If the conductor has different values of current flowing down its length due to current division
the equation has to consider the different (reduced) currents flowing down each section of the
conductor. In that case:
s = k i (k c1 × l 1 + k c2 × l 2 +....+ k cn × l n )
(E.2)
The point of the strike, essential for k c, and the point where the separation distance is to be
considered, may be different.
E.4.2.4.2
Structure with a cantilevered part
To reduce the probability of a person standing under a cantilevered construction from
becoming an alternate path for lightning current flowing in the down-conductor running on the
cantilevered wall, the actual distance, d, in metres should satisfy the following condition:
d > 2,5 + s
(E.3)
where s is the separation distance in metres calculated in accordance with 6.3.
The value 2,5 is representative of the height at the tips of a man's fingers when he stretches
his arm vertically (see Figure E.3).
LPS
l
l
s
d
>2,5 m
m
>2,5
IEC 2109/05
d Actual distance > s
s Separation distance according to 6.3
l Length for the evaluation of separation distance s
NOTE
The height of the person with raised hand is taken to be 2,5 m.
Figure E.3 – LPS design for a cantilevered part of a structure
62305-3 © IEC:2006
– 125 –
Loops in a conductor as shown in Figure 1 can produce high inductive voltage drops, which
can cause a lightning discharge to pass through a structure wall thereby causing damage.
If the conditions in 6.3 are not met, arrangements should be made for direct routing through
the structure at the points of re-entrant lightning conductor loops for those conditions shown
in Figure 1.
E.4.3
Reinforced concrete structures
E.4.3.1
General
Industrial structures frequently comprise sections of reinforced concrete which are produced
on site. In many other cases, parts of the structure may consist of prefabricated concrete
units or steel parts.
Steel reinforcement in reinforced concrete structures conforming to 4.3 may be used as a
natural component of the LPS.
Such natural components must fulfil the requirements of:
–
down-conductors according to 5.3;
–
earth-termination networks according to 5.4.
Moreover, the conductive reinforcement of concrete, when properly used, should form the
cage for potential equalization of the internal LPS according to 6.2.
Furthermore, the steel reinforcement of the structure, if adequate, may serve as an electromagnetic shield, which assists in protecting electrical and electronic equipment from
interference caused by lightning electromagnetic fields according to IEC 62305-4.
If the reinforcement of the concrete and any other steel constructions of a structure are
connected both externally and internally so that the electrical continuity conforms to 4.3,
effective protection may be achieved against physical damage.
The current injected into the reinforcing rods is assumed to flow through a large number of
parallel paths. The impedance of the resulting mesh is thus low and, as a consequence, the
voltage drop due to the lightning current is also low. The magnetic field generated by the
current in the reinforcing steel mesh is weak due to the low current density and the parallel
current paths generating opposing electromagnetic fields. Interference with neighbouring
internal electrical conductors is correspondingly reduced.
NOTE
For protection against electromagnetic interference, see IEC 62305-4 and IEC 61000-5-2.
When a room is totally enclosed by steel-reinforced concrete walls whose electrical continuity
conforms to 4.3, the magnetic field due to lightning current flowing through the reinforcement
in the vicinity of the walls is lower than that in a room of a structure protected with
conventional down-conductors. Owing to the lower induced voltages in conductor loops
installed inside the room, protection against failures of internal systems may be easily
improved.
After the construction phase, it is nearly impossible to determine the layout and construction
of the reinforcement steel. Therefore, the layout of the reinforcement steel for the purpose of
lightning protection should be very well documented. This can be done utilizing drawings,
descriptions and photographs taken during the construction.
62305-3 © IEC:2006
E.4.3.2
– 127 –
Utilization of reinforcement in concrete
Bonding conductors or grounding plates should be furnished in order to provide reliable
electrical connection to the reinforcement steel.
Conductive frames that, for example, are attached to the structure may be used as natural
LPS conductors and as connection points for the internal equipotential bonding system.
A practical example is the use of foundation anchors or foundation rails of machines,
apparatus or housings, to achieve potential equalization. Figure E.4 illustrates the
arrangement of the reinforcement and the bonding bars in an industrial structure.
1
2
3
4
7
6
4
5
5
9
6
7
8
IEC 2110/05
1
2
3
4
5
Key
Electrical power equipment
Steel girder
Metal covering of the facade
Bonding joint
Electrical or electronic equipment
6
7
8
9
Bonding bar
Steel reinforcement in concrete (with superimposed
mesh conductors)
Foundation earth electrode
Common inlet for different services
Figure E.4 – Equipotential bonding in a structure with a steel reinforcement
62305-3 © IEC:2006
– 129 –
The location of bonding terminations in the structure should be specified at an early planning
stage in the design of the LPS and should be made known to the civil works contractor.
The building contractor should be consulted to determine whether welding to the reinforcing
rods is permitted, whether clamping is possible or whether additional conductors should be
installed. All necessary work should be performed and inspected prior to pouring of the
concrete (i.e. planning of the LPS should be carried out in conjunction with the design of the
structure).
E.4.3.3
Welding or clamping to the steel-reinforcing rods
The continuity of the reinforcing rods should be established by clamping or welding.
NOTE
Clamps conforming to EN 50164-1 may be considered suitable.
Welding to the reinforcing rods is only permitted if the civil works designer consents. The
reinforcing rods should be welded over a length not less than 30 mm (see Figure E.5).
1
1
2
2
1
2
IEC 2111/05
Key
1 Reinforcing bars
2 Welded seam at least 30 mm long
Figure E.5 – Welded joints of reinforcing rods in reinforced concrete, if permitted
62305-3 © IEC:2006
– 131 –
The connection to outside components of the lightning protection system should be
established by a reinforcement rod brought out through the concrete at a designated location
or by a connecting rod or ground plate passing through the concrete which is welded or
clamped to the reinforcing rods.
Where joints between the reinforcing rods in concrete and the bonding conductor are made by
means of clamping, two bonding conductors (or one bonding conductor with two clamps to
different reinforcing bars) should always be used for safety reasons, since the joints cannot
be inspected after the concrete has set. If the bonding conductor and reinforcing rod are
dissimilar metals, then the joint area should be completely sealed with a moisture inhibiting
compound.
Figure E.6 shows clamps used for joints for reinforcing rods and solid tape conductors.
Figure E.7 shows details for connection of an external system to reinforcing rods.
The bonding conductors should be dimensioned for the proportion of lightning current flowing
at the bonding point (see Tables 8 and 9).
1
3
2
IEC 2112/05
Figure E.6a – Circular conductor to a reinforcing rod
3
1
4
IEC 2113/05
Figure E.6b – Solid tape conductor to a reinforcing rod
Key
1 Reinforcing rod
2 Circular conductor
3 Screw
4 Tape conductor
Figure E.6 – Example of clamps used as joints
between reinforcing rods and conductors
62305-3 © IEC:2006
– 133 –
1
4
2
5
8
3
IEC 2115/05
IEC 2114/05
Figure E.7a
Figure E.7b
6
7
8
3
3
IEC 2117/05
IEC 2116/05
Figure E.7c
Figure E.7d
Key
1 Bonding conductor
2 Nut welded to steel bonding connector
3 Steel-bonding connector*
4 Cast in non ferrous bonding point
5 Stranded copper bonding connector
6 Corrosion protection measure
7 C-steel (C-shaped mounting bar)
8 Welding
* The steel-bonding connector is connected at many points by welding or clamping to the steel reinforcing bars.
NOTE Construction shown in Figure E.7c is not a generally accepted solution in terms of good engineering
practice.
Figure E.7 – Examples for connection points to the reinforcement
in a reinforced concrete wall
62305-3 © IEC:2006
E.4.3.4
– 135 –
Materials
The following materials can be used as additional conductors installed in concrete for
lightning protection purposes: steel, mild steel, galvanized steel, stainless steel and copper.
The use of galvanized steel rods in concrete is sometimes not permitted by the civil works
contractor. This is based on a misunderstanding. The reinforcement steel is made passive by
the concrete, resulting in a high potential protecting it from corrosion.
In order to avoid confusion between the different types of steel rods in concrete, it is
recommended that round steel rods of at least 8 mm diameter with a smooth surface be used
as additional conductors in contrast to the ordinary ribbed surface of the reinforcing rods.
E.4.3.5
Corrosion
Where steel reinforcement bonding conductors are brought through a concrete wall, particular
attention should be paid to protection against chemical corrosion.
The simplest corrosion protection measure is the provision of a silicon rubber or bitumen
finish in the vicinity of the exit point from the wall, e.g. 50 mm or more in the wall and 50 mm
or more outside the wall (see Figure E.7c).
Where copper bonding conductors are brought through the concrete wall, there is no
corrosion risk if a solid conductor, proprietary bonding point, PVC covering, or insulated wire
is used (see Figure E.7b). For stainless steel bonding conductors, in accordance with
Tables 6 and 7, no corrosion prevention measures need to be used.
In the case of extremely aggressive atmospheres, it is recommended that the bonding
conductor projecting from the wall be made of stainless steel.
NOTE Galvanized steel outside of the concrete in contact with reinforcement steel in the concrete may, under
certain circumstances, cause damage to the concrete.
When cast-in type nuts or mild steel pieces are used, these should be protected against
corrosion on the outside of the wall. Serrated lock washers should be used to make electrical
contact through the protective finish of the nut (see Figure E.7a).
For more information on corrosion protection, see E.5.6.2.2.2.
E.4.3.6
Connections
Investigations show that lashing is not suitable for lightning-current-carrying connections.
There is a risk of the lashing wire exploding and damaging the concrete. However, on the
basis of earlier investigations it can be assumed that at least every third wire lashing forms an
electrically conductive link, so that practically all the rods of the reinforcement are electrically
interconnected. Measurements carried out on reinforced concrete structures support this
conclusion.
So for lightning-carrying connections welding and clamping are the preferred methods.
Lashing as a connection is suitable for additional conductors for equipotentialization and for
EMC purposes only.
Connections of external circuits to the interconnected reinforcement should be performed by
means of clamps or by welding.
62305-3 © IEC:2006
– 137 –
Welds within concrete should be at least 30 mm long. Crossing rods should be bent to run for
at least 50 mm in parallel prior to welding.
When welded rods need to be cast into concrete, it is not sufficient to weld at crossing points
with weld seam lengths of only a few millimetres. Such joints frequently break when the
concrete is poured.
Figure E.5 shows correct welding of bonding conductors to the reinforcing rods of the
reinforced concrete.
Where welding to the reinforcing rods is not permitted, clamps or additional dedicated
conductors should be used. These additional conductors can be made of steel, mild steel,
galvanized steel or copper. The additional conductors should be connected to a large number
of reinforcing rods by lashings and clamps to take advantage of the shielding possibilities of
the reinforcement steel.
NOTE Where welding is permitted, both conventional welding and exothermic welding are acceptable together
with the appropriate welding methods.
E.4.3.7
Down-conductors
The reinforcing rods of walls or concrete columns and steel structural frames may be used as
natural down-conductors. A termination joint should be provided on the roof to facilitate the
connection of the air-termination system and, unless the reinforced concrete foundation is
being used as the only earth termination, termination joints should be provided to facilitate the
connection with the earth-termination system.
When using a particular rod of the reinforcement steel as the down-conductor, care should be
taken in the route to earth to ensure that the rod that is located in the same position will be
used all the way down, thereby providing direct electrical continuity.
When the vertical continuity of the natural down-conductors, providing a straight path from
roof to ground cannot be guaranteed, additional dedicated conductors should be used. These
additional conductors should be lashed to the reinforcement steel.
Wherever there is doubt as to the most direct route for the down-conductor (i.e. for existing
buildings) an external down-conductor system should be added.
Figures E.4 and E.8 show construction details of natural components in the LPS for reinforced
concrete structures. See also E.5.4.3.2 for the use of the rods of reinforced concrete elements
as foundation earth electrodes.
62305-3 © IEC:2006
– 139 –
b
2
3
1
4
6
5
c
5
a
7
7
7
8
5
9
10
IEC 2118/05
Key
1
Metallic covering of the roof parapet
2
Joint between façade plates and air-termination
3
Horizontal air-termination conductor
4
Metallic façade segment covering
5
Equipotentialization bar of the internal LPS
6
Joint between façade plates
7
Test joint
8
Steel reinforcement in concrete
9
Type B ring earth electrode
10
Foundation earth electrode
An applicable example may utilize the following dimensions a = 5 m b = 5 m c = 1 m.
NOTE
For the joints between the plates, see Figure E.35.
Figure E.8a – Use of a metallic façade covering as a natural down-conductor system on a structure of steel
reinforced concrete
62305-3 © IEC:2006
– 141 –
1
2
3
4
IEC 2119/05
Key
1
Vertical frame
2
Wall fixing
3
Connectors
4
Horizontal frame
Figure E.8b – Connection of facade supports
Figure E.8 – Use of metallic facade as natural down-conductor system
and connection of facade supports
Internal down-conductors in the individual columns and the walls should be interconnected by
means of their steel reinforcing rods and should conform to the conditions for electrical
continuity according to 4.3.
Steel reinforcing rods of individual prefabricated concrete elements and the reinforcing rods of
concrete columns and concrete walls should be connected to the reinforcing rods of floors
and roofs before the floors and roofs are cast.
Extensive continuously conductive parts exist within the reinforcing of all constructional
elements, which are cast with concrete on site, for example, walls, columns, stairs and lift
shafts. If floors are constructed of site-cast concrete, the down-conductors in the individual
columns and walls should be interconnected by means of their reinforcing rods to ensure an
even distribution of the lightning current. If floors are constructed of prefabricated concrete
elements, such connections are generally not available. However, at little extra cost it is
generally possible to prepare joints and terminations to connect the reinforcing rods of the
individual prefabricated concrete elements to the reinforcing rods of the columns and walls
before the floors are cast by insertion of additional connecting rods.
Prefabricated concrete elements used as suspended facades are not effective for lightning
protection as bonding connections are not provided. If highly effective lightning protection is
to be provided for equipment installed within a structure, such as office buildings with
extensive information-processing equipment and computer networks, it is necessary for the
reinforcing rods of such facade elements to be interconnected and connected to the
reinforcing rods of the load-bearing elements of the structure in such a manner that the
lightning current can flow through the complete outer surface of the structure (see
Figure E.4).
62305-3 © IEC:2006
– 143 –
If continuous strip windows are installed in the outer walls of a structure, it is essential that a
decision be taken as to whether the connection of the prefabricated concrete parts above and
below the continuous strip windows should be made by means of the existing columns or
whether they should be interconnected at smaller intervals corresponding to the window pitch.
Extensive integration of conductive parts of the outer walls improves the electromagnetic
shielding of the interior of the structure. Figure E.9 shows the connection of a continuous strip
windows to a metal facade covering.
2
1
+
+
+
+
+
+
1
3
4
4
+
+
5
+
+
+
+
1
3
IEC 2120/05
Key
1 Joint between a façade plate segment and the metallic strip window
2 Metallic façade plate
3 Horizontal metallic strip
4 Vertical metallic strip
5 Window
Figure E.9 – Connection of the continuous strip windows to a metal façade covering
If steel structures are used as down-conductors, every steel column should be connected to
the steel reinforcing rods of the concrete foundation by bonding points as shown in
Figure E.7. Steel bonding bars within the reinforced concrete of a structure should be
interconnected by means of vertical conductors which should be manufactured of mild steel
suitable for welding. New structures of steel-reinforced concrete should be constructed in
accordance with 4.3.
NOTE For more information on the use of steel reinforcement of structure walls for the purpose of electromagnetic shielding, see IEC 62305-4.
In the case of large, low buildings such as halls, the roof is supported not only at the building
circumference but also by internal columns. Conductive portions of the columns should be
connected to the air-termination system at the top and to the equipotential bonding system at
the floor, creating internal down-conductors. Increased electromagnetic interference occurs in
the vicinity of such internal down-conductors.
62305-3 © IEC:2006
– 145 –
Steel skeleton constructions generally use steel roof girders connected by means of bolted
joints. Provided the bolts are tightened with the force required to achieve mechanical
strength, all bolted steel parts may be considered electrically interconnected. The thin paint
layer is pierced by the lightning current on initial discharge thus forming a conductive bridge.
The electrical connection may be improved by baring the seating surface of the bolt heads,
bolt nuts and washers. A further improvement can be achieved by provision of a welding seam
approximately 50 mm long after completion of the structural assembly.
On existing structures with extensive conductive parts in/on the outer walls, the continuity of
conductive parts should be established for use as down-conductors. This technique is also
recommended when high demands on the cultural aspects of architectural design have to be
maintained in addition to the demands for protection against LEMP.
Interconnected equipotentialization bars should also be provided. Each equipotentialization
bar should be connected to the conductive parts in the outer walls and in the floor. This may
already be provided by the horizontal reinforcing bars at the ground level and each
subsequent floor level.
If possible, a connection point to the steel reinforcement in the floor or in the wall should be
provided. The connection should be made to at least three reinforcing rods.
In large structures, the equipotentialization bar acts as a ring conductor. In such cases
connection points to the steel-reinforcing bars should be made every 10 m. Other than
measures which may be prescribed for the basement, no other special measures to connect
the reinforcement of the structure to the LPS are necessary.
E.4.3.8
Equipotentialization
When a large number of bonding connections to the reinforcement is required at different
floors and a significant interest is given to achieve current paths of low inductance utilizing
the reinforcing rods of the concrete walls for potential equalization and for shielding of the
inner space of the structure, ring-conductors should be installed within or outside the concrete
on the separate floors. These ring conductors should be interconnected by means of vertical
rods at intervals not greater than 10 m.
This arrangement should be given preference due to its greater reliability, especially where
the magnitude of the interference current is unknown.
A meshed-connection conductor network is also recommended. Connections should be
designed to carry high currents in the event of a fault in the energy supply.
E.4.3.9
Foundation as earth-termination
For large structures and industrial plants the foundation is normally reinforced. The reinforcing
rods of the foundation, foundation slab and outer walls in the region below the soil surface of
such structures form an excellent foundation earth electrode, provided the requirements of 5.4
are satisfied.
The reinforcing rods of the foundation and the buried walls can be used as a foundation earth.
This method achieves good earthing at minimum cost. In addition, the metal enclosure,
consisting of the steel reinforcement of the structure, in general offers a good potential
reference for the electric power supply, telecommunication and electronic installations of the
structure.
62305-3 © IEC:2006
– 147 –
In addition to the interconnection of the reinforcing rods by wire-lashing, the installation of an
additional meshed metal network to ensure good joints is recommended. This additional
network should also be lashed to the reinforcement steel. The terminal conductors for
connections of external down-conductors or structure elements used as down-conductors and
for connection of the earth-termination installed externally should be brought out of the
concrete at suitable points.
In general, the reinforcing of a foundation is electrically conductive except in cases where
gaps are provided between different parts of the structure to allow different settling rates.
Gaps between conductive structure parts should be bridged by bonding conductors
conforming to Table 6 using clamps and joints in accordance with 5.5.
Reinforcing rods of concrete columns, piers and walls standing on a foundation should be
connected to the reinforcing rods of the foundation and to the conductive parts of the roof.
Figure E.10 shows the design of the LPS of a reinforced concrete structure for concrete piers,
walls and a roof with conductive parts.
62305-3 © IEC:2006
– 149 –
1
2
3
1
2
IEC 2121/05
Key
1 LPS conductor passing a watertight bushing
2 Steel reinforcement in a concrete column
3 Steel reinforcement in concrete walls
NOTE The steel reinforcing of an internal column becomes a natural internal down-conductor when the steel
reinforcing of the column is connected to the air-termination and the earth-termination of the LPS. The
electromagnetic environment near the column should be considered when sensitive electronic equipment is
installed near the column.
Figure E.10 – Internal down-conductors in industrial structures
When welding to reinforcing is not allowed, additional conductors should be installed in the
piers, or the connections should be implemented by means of tested joints. These additional
conductors should be lashed to the reinforcing steel.
62305-3 © IEC:2006
– 151 –
After completion of construction and connecting all the services to the building via an equipotential bonding bar, it will often be impossible in practice to measure the earthing resistance
as part of the maintenance programme.
If in certain conditions it is not possible to measure the earthing resistance of the foundation
earth, the installation of one or more reference earth electrodes close to the structure provide
a possible method of monitoring the changes in the environment of the earthing system over
the years by performing a circuit measurement between the earth electrode and the
foundation earthing system. However, good equipotentialization is the main advantage of the
foundation earthing system and the resistance to earth tends to be less important.
E.4.3.10
Installation procedures
All lightning protection conductors and clamps should be installed by the installer of the LPS.
Agreement should be reached with the civil works contractor in sufficient time to ensure that
the time schedule for construction work is not exceeded as a result of delay in installation of
the LPS before pouring the concrete.
During construction, measurements should be taken regularly and an LPS installer should
supervise the construction (see 4.3).
E.4.3.11
Prefabricated reinforced concrete parts
If prefabricated reinforced concrete parts are used for lightning protection, e.g. as downconductors for shielding or as conductors for potential equalization, connection points
according to Figure E.7 should be attached to them to allow later interconnection of the
prefabricated reinforcement with the reinforcement of the structure in a simple manner.
The location and form of connection points should be defined during the design of the
prefabricated reinforced concrete parts.
The connection points should be located so that in the prefabricated concrete part a
continuous reinforcing rod runs from one bonding joint to the next.
When the arrangement of continuous reinforcing rods in a prefabricated reinforced concrete
part is not possible with standard reinforcing rods, an additional conductor should be installed
and lashed to the existing reinforcement.
In general, one connection point and a bonding conductor is required at each corner of a
plate-like prefabricated reinforced concrete part as illustrated in Figure E.11.
E.4.3.12
Expansion joints
When the structure comprises a number of sections with expansion joints, with allowance for
settling of the structure sections, and extensive electronic equipment is to be installed in the
building, bonding conductors should be provided between the reinforcement of the various
structural sections across the expansion joints at intervals not exceeding one half of the
distance between the down-conductors specified in Table 4.
In order to ensure low-impedance potential equalization and effective shielding of the space
inside a structure, expansion joints between sections of a structure should be bridged at short
intervals (between 1 m and one half of the distance between down-conductors) by flexible or
sliding bonding conductors depending on the required shielding factor, as shown in
Figure E.11.
62305-3 © IEC:2006
– 153 –
1
2
IEC 2122/05
Key
1 Reinforced precast concrete
2 Bonding conductors
Figure E.11a – Installation of bonding conductors on plate-like prefabricated reinforced concrete parts by
means of bolted or welded conductor links
1
A
B
4
3
2
IEC 2123/05
Key
1 Expansion slot
2 Welded joint
3 Recess
4 Flexible bonding conductor
A Reinforced concrete part 1
B Reinforced concrete part 2
Figure E.11b – Construction of flexible bonds between two reinforced concrete parts bridging an expansion
slot on a structure
Figure E.11– Installation of bonding conductors in reinforced concrete structures and
flexible bonds between two reinforced concrete parts
62305-3 © IEC:2006
E.5
– 155 –
External lightning protection system
E.5.1
General
E.5.1.1
Non-isolated LPS
In most cases, the external LPS may be attached to the structure to be protected.
When the thermal effects at the point of strike or on conductors carrying the lightning current
may cause damage to the structure, or to the content of the structure to be protected, the
spacing between LPS conductors and combustible material should be at least 0,1 m.
NOTE
Typical cases are
−
−
structures with combustible coverings,
structures with combustible walls.
The positioning of external LPS conductors is fundamental to the design of the LPS and
depends on the shape of the structure to be protected, the level of protection required and the
geometric design method employed. The air-termination system design generally dictates the
design of the down-conductor system, the earth-termination system and the design of the
internal LPS.
If adjacent buildings have an LPS, those LPS should be connected to the LPS of the building
under consideration.
E.5.1.2
Isolated LPS
An isolated external LPS should be used when the flow of the lightning current into bonded
internal conductive parts may cause damage to the structure or its contents.
NOTE The use of an isolated LPS may be convenient where it is predicted that changes in the structure may
require modifications to the LPS.
LPS that are connected to conductive structural elements and to the equipotential bonding
system only at ground level, are defined as isolated according to 3.3.
Isolated LPS are achieved either by installing air-termination rods or masts adjacent to the
structure to be protected or by suspending overhead wires between the masts in accordance
with the separation distance of 6.3.
Isolated LPS are also installed on structures of insulating material, such as brickwork or
wood, where the separation distance, as defined in 6.3, is maintained and no connection is
made to conductive parts of the structure nor to equipment installed therein, with the
exception of connections to the earth-termination system at ground level.
Conductive equipment within the structure and electrical conductors should not be installed
with distances to the air-termination system conductors and to the down-conductors shorter
than the separation distance defined in 6.3. AII future installations should conform to the
requirements of an isolated LPS. These requirements should be made known to the owner of
the structure by the contractor responsible for the design and construction of the LPS.
62305-3 © IEC:2006
– 157 –
The owner should inform future contractors performing work in or on the building about these
requirements. The contractor responsible for such work should inform the owner of the
structure if the contractor cannot meet these requirements.
AII parts of equipment installed in a structure with an isolated LPS should be placed within the
protected space of the LPS and satisfy the separation distance conditions. The LPS
conductors should be mounted on insulated conductor fixtures, if conductor fixings attached
directly to the structure walls are too close to conductive parts, so that the distance between
the LPS and the inner conductive parts exceed the separation distance as defined in 6.3.
Flush-mounted conductive roof fixtures which are not connected to the equipotential bonding
and have a distance to the air-termination system not in excess of the separation distance but
a distance to the equipotential bonding in excess of the separation distance, should be
connected to the air-termination system of the isolated LPS.
The design of an LPS and the safety instructions for work in the vicinity of a roof fixture
should take account of the fact that the voltage on such fixtures will rise to that of the airtermination system in the event of a lightning strike.
Isolated LPS should be installed on structures with extensive interlinked conductive parts
when it is desired to prevent lightning current from flowing through structure walls and
internally installed equipment.
On structures consisting of continuously interlinked conductive parts such as steel
construction or steel-reinforced concrete, the isolated LPS should maintain the separation
distance to these conductive parts of the structure. To achieve adequate separation, LPS
conductors may have to be fixed to the structure by insulated conductor fixtures.
It should be noted that columns and ceilings of reinforced concrete are often used in brick
structures.
E.5.1.3
Dangerous sparking
Dangerous sparking between
installations can be avoided
an
LPS
and
metal,
electrical
and
telecommunication
–
in an isolated LPS by insulation or separation according to 6.3,
–
in a non-isolated LPS by equipotential bonding, according to 6.2, or by insulation or
separation according to 6.3.
E.5.2
E.5.2.1
Air-termination systems
General
This standard does not provide any criteria for the choice of the air-termination system
because it considers rods, stretched wires and meshed conductors as equivalent.
The arrangement of an air-termination system should be in accordance with the requirements
of Table 2.
E.5.2.2
Positioning
For the design of the air-termination system, the following methods should be used,
independently or in any combination, providing that the zones of protection afforded by
different parts of the air-termination overlap and ensure that the structure is entirely protected
according to 5.2:
62305-3 © IEC:2006
–
protection angle method;
–
rolling sphere method;
–
mesh method.
– 159 –
AII three methods may be used for the design of an LPS. The choice of class of LPS depends
on a practical evaluation of its suitability and the vulnerability of the structure to be protected.
The positioning method may be selected by the LPS designer. However, the following
considerations may be valid:
–
the protection angle method is suitable for simple structures or for small parts of bigger
structures. This method is not suitable for structures higher than the radius of the rolling
sphere relevant to the selected protection level of the LPS;
–
the rolling sphere method is suitable for complex shaped structures;
–
the mesh method is for general purposes and it is particularly suitable for the protection of
plane surfaces.
The air-termination design method and LPS design methods used for the various parts of the
structure should be explicitly stated in the design documentation.
E.5.2.2.1
Protection angle method
Air-termination conductors, rods, masts and wires should be positioned so that all parts of the
structure to be protected are inside the envelope surface generated by projecting points on
the air-termination conductors to the reference plane, at an angle α to the vertical in all
directions.
The protective angle α should conform to Table 2, with h being the height of the airtermination above the surface to be protected.
A single point generates a cone. Figures A.1 and A.2 show how the protected space is
generated by the different air-termination conductors in the LPS.
According to Table 2, the protective angle α is different for different heights of air-termination
above the surface to be protected (see Figures A.3 and E.12).
62305-3 © IEC:2006
– 161 –
α1
h1
h1
α2
h2
H
IEC 2124/05
Key
H
h1
Height of the building over the ground reference plane
Physical height of an air-termination rod
+ H , being the height of the air-termination rod over the ground
h2
h
α1
The protective angle corresponding to the air-termination height h= h 1 , being the height above the roof
surface to be measured (reference plane)
α2
The protective angle corresponds to the height h 2
1
Figure E.12 – Protective angle method air-termination design
for different heights according to Table 2
The protective angle method has geometrical limits and cannot be applied if h is larger than
the rolling sphere radius, r, as defined in Table 2.
If structures on the roof are to be protected with finials and the protective volume of the finials
is over the edge of the building, the finials should be placed between the structure and the
edge. If this is not possible the rolling sphere method should be applied.
The design of air-termination using the protection angle air-termination design method is also
shown in Figures E.13 and E.14 for an isolated LPS and in Figures E.15 and E.16 for a nonisolated LPS.
62305-3 © IEC:2006
– 163 –
4
α1
α1
s
s
α2
α2
1
1
22
3
IEC 2125/05
Key
1 Air-termination mast
2 Protected structure
3 Ground being the reference plane
4 Intersection between protective cones
s Separation distance according to 6.3
α 1 , α 2 Protective angle complying with Table 2
Figure E.13a – Projection on a vertical plane
1
2
IEC 2126/05
NOTE
The two circles denote the protected area on the ground as the reference plane.
Figure E.13b – Projection on the horizontal reference plane
Figure E.13 – Isolated external LPS using two isolated air-termination masts designed
according to the protective angle air-termination design method
62305-3 © IEC:2006
– 165 –
4
4
α
s1
α
s2
s2
1
α
α
s1
2
1
3
3
2
1
IEC 2127/05
IEC 2128/05
Figure E.14b – Projection on a vertical plane
perpendicular to the plane containing the two
masts
Figure E.14a – Projection on a vertical plane
containing the two masts
4
1
2
3
IEC 2129/05
Figure E.14c – Projection on the horizontal
reference plane
Key
1
2
3
4
s1, s2
α
Air-termination mast
Protected structure
Protected area on the reference plane
Horizontal wire air-termination
Separation distances according to 6.3
Protective angle complying with Table 2
NOTE The air-termination system is designed according to the protective angle air-termination design method.
The whole structure should be inside the protected volume.
Figure E.14 – Isolated external LPS using two isolated air-termination masts,
interconnected by horizontal catenary wire
62305-3 © IEC:2006
– 167 –
1
1
α
α
3
2
2
IEC 2130/05
Key
1 Air-termination rod
2 Protected structure
3 Assumed reference plane
α Protective angle complying with Table 2
Figure E.15a – Example using one air-termination rod
1
1
α
α
α
2
3
2
IEC 2131/05
Key
1 Air-termination rod
2 Protected structure
3 Assumed reference plane
α Protective angle complying with table 2
Figure E.15b– Example using two air-termination rods
NOTE
The whole structure should be inside the protected volumes of the air-termination rods.
Figure E.15 – Example of design of an air-termination of a non-isolated LPS by
air-termination rods
62305-3 © IEC:2006
– 169 –
d1
α
IEC 2132/05
Key
α Protective angle complying with Table 2
d 1 Distance of horizontal wire from the roof
Figure E.16a – Projection on the vertical plane perpendicular to the plane containing the conductor
d1
IEC 2133/05
Key
α Protective angle complying with Table 2
NOTE
The whole structure should be inside the protected volume.
Figure E.16b – Projection on a vertical plane containing the conductor
Figure E.16 – Example of design of an air-termination of a non isolated LPS by a
horizontal wire according to the protective angle air-termination design method
If the surface on which the air-termination system is placed is inclined, the axis of the cone
which forms the protected zone is not necessarily the air-termination rod, but is instead the
perpendicular to the surface on which the air-termination rod is placed; with the top of the
cone being equal to the top of the air-termination rod (see Figure E.17).
62305-3 © IEC:2006
– 171 –
4
B’
B
ht
r
1
h’
r
h
1
C’
C
O
2
IEC 2134/05
Figure E.17a – Protected volume of a mast on a sloped surface using the rolling
sphere design method (h t > r)
3
α
2
h = ht
1
D’
1
90o
D
IEC 2135/05
Figure E.17b – Protected volume of an air-termination rod on a sloped surface
using the protection angle design method
Key
1
2
3
4
r
h, h’
ht
α
Protected volume
Reference plane
Air-termination rod
Mast
Radius of the rolling sphere according to Table 2
Relevant heights of air-termination according to Table 2
Physical height of the mast above the reference plane
Protection angle
B, C, B’, C’ Touching points with the rolling sphere
C, C’,D, D’ Limit of the protected area
NOTE The heights h and h’ should be less than h t . Two values of h, e.g. h and h’ are applicable on a sloped
reference plane.
Figure E.17 – Protected volume of an air- termination rod or mast on a sloped surface
62305-3 © IEC:2006
E.5.2.2.2
– 173 –
Rolling sphere method
The rolling sphere method should be used to identify the protected space of parts and areas
of a structure when Table 2 excludes the use of the protective angle method.
Applying this method, the positioning of an air-termination system is adequate if no point of
the volume to be protected is in contact with a sphere of radius, r, rolling on the ground,
around and on top of the structure in all possible directions. Therefore, the sphere should
touch only the ground and/or the air-termination system.
The radius r of the rolling sphere depends on the class of LPS (see Table 2).
Figures E.18 and E.19 show the application of the rolling sphere method to different
structures. The sphere of radius r is rolled around and over all the structure until it meets the
ground plane or any permanent structure or object in contact with the ground plane which is
capable of acting as a conductor of lightning. A striking point could occur where the rolling
sphere touches the structure and at such points protection by an air-termination conductor is
required.
62305-3 © IEC:2006
– 175 –
Air termination
r
r
r
IEC 2136/05
r
Radius of the rolling sphere according to Table 2.
NOTE Air-termination LPS conductors are installed on all points and segments which are in contact with the
rolling sphere, whose radius complies with the selected protection level except for the lower part of the structure in
accordance with 5.2.3.
Figure E.18a – Design of an LPS air-termination according to the rolling sphere method
1
2
α
3
h
4
5
IEC 2137/05
Key
1 Air-termination conductor
2 Air-termination rod
3 Mesh size
4 Down-conductor
5 Earthing system with ring conductor
h Height of the air-terminal above ground level
α Protective angle
Figure E.18b – General arrangement of air-termination elements
Figure E.18 – Design of an LPS air-termination according to the rolling sphere method,
protective angle method, mesh method and general arrangement
of air-termination elements
62305-3 © IEC:2006
– 177 –
1
1
r
r
r
2
r
r
r
r
1
IEC 2138/05
Key
1
Shaded areas, are exposed to lightning interception and need protection according Table 2
2
Mast on the structure
r
Radius of rolling sphere according to Table 2
NOTE
Protection against side flashes is required according to 5.2.3 and A.2.
Figure E.19 – Design of an LPS air-termination conductor network on a structure
with complicated shape
When the rolling sphere method is applied to drawings of the structure, the structure should
be considered from all directions to ensure that no part protrudes into an unprotected zone –
a point which might be overlooked if only front, side and plan views on drawings are
considered.
The protected space generated by an LPS conductor is the volume not penetrated by the
rolling sphere when it is in contact with the conductor and applied to the structure.
Figure E.18 shows the protection afforded by an LPS air-termination system according to the
mesh method, rolling sphere method and protection angle method with a general arrangement
of air-termination elements.
In the case of two parallel horizontal LPS air-termination conductors placed above the
horizontal reference plane in Figure E.20, the penetration distance p of the rolling sphere
below the level of the conductors in the space between the conductors may be calculated:
p = r – [r 2 – (d/2) 2 ] 1/2
(E.4)
The penetration distance p should be less than h t minus the height of objects to be protected
(the motor in Figure E.20).
62305-3 © IEC:2006
– 179 –
r
1
1
p
ht = h
2
3
d
IEC 2139/05
Key
1
Horizontal wires
2
Reference plane
3
Space protected by two parallel air-termination horizontal wires or two air-termination rods
ht
Physical height of the air-termination rods above the reference plane
p
Penetration distance of the rolling sphere
h
Height of the air-termination according to Table 2
r
Radius of the rolling sphere
d
Distance separating two parallel air-terminal horizontal wires or two air-terminal rods
NOTE The penetration distance p of the rolling sphere should be less than h t minus the largest height of objects
to be protected, in order to protect objects in the space between the terminations.
Figure E.20 – Space protected by two parallel air-termination horizontal wires
or two air-termination rods (r > h t )
The example shown in Figure E.20 is also valid for three or four air-termination rods; for
example, four vertical rods placed at the corners of a square with the same applied height h.
In this case, d in Figure E.20 corresponds to the diagonals of the square formed by the four
rods.
NOTE Since the mid 1930s, it has been known that the radius of the rolling sphere is correlated with the peak
value of the current in the lightning that strikes the structure: r = 10 I 0,65 where I is defined as kA.
62305-3 © IEC:2006
– 181 –
The points at which lightning will strike can be determined using the rolling sphere method.
The rolling sphere method can also identify the probability of occurrence of a strike to each
point of the building.
Figure E.21 shows a building over which the rolling sphere rolls . The dashed line depicts the
path of the centre of the rolling sphere. This is also the geometrical location of the tip of the
downward leader, from which the final discharge ensues. All those lightning flashes with tips
lying on the path of the centre of the rolling sphere will discharge to the nearest point of the
building. Around the edges of the roof there is a quarter circular path with possible positions
of the tip of the downward leader which will discharge to the edge of the building. This shows
that a considerable portion of the strikes will occur at the edge of the roof, some at the walls
and some at the roof surface.
62305-3 © IEC:2006
– 183 –
r
R
R
R
r
r
IEC 2140/05
r
Radius of the rolling sphere according to Table 2
Figure E.21a – Side view
r
R
r
r
IEC 2141/05
r
Radius of the rolling sphere according to Table 2
Figure E.21b – Plan view
Figure E.21 – Points at which lightning will strike a building
62305-3 © IEC:2006
– 185 –
In order to make a prediction about the overall possibility of a strike to the wall, the plan view
must also be considered (see Figure E.21b).
E.5.2.2.3
Mesh method
For the purpose of protecting flat surfaces, a mesh is considered to protect the whole surface
if the following conditions are fulfilled.
a) As mentioned in Annex A, air-termination conductors are positioned on
–
roof edge lines,
–
roof overhangs,
–
roof ridge lines, if the roof slope exceeds 1/10,
–
the lateral surfaces of the structure higher than 60 m at levels higher than 80 % of the
height of the structure;
b) the mesh dimensions of the air-termination network are not greater than the values given
in Table 2;
c) the network of the air-termination system is accomplished in such a way that the lightning
current will always encounter at least two distinct metallic routes to the earth and no metal
installation protrudes outside the volume protected by air-termination systems;
NOTE A larger number of down-conductors results in reduction of the separation distance and reduces the
electromagnetic field within the building (see 5.3).
d) the air-termination conductors follow as far as possible short and direct routes.
Examples of non-isolated LPS using the air-termination mesh method design are shown in
Figure E.22a for a flat-roof structure and in Figure E.22b for a sloped-roof structure.
Figure E.22c shows an example of an LPS on a industrial building. Figure E.22d shows an
example of an LPS with concealed conductors.
62305-3 © IEC:2006
– 187 –
w
IEC 2142/05
Figure E.22a – LPS air-termination on a flat-roof structure
w
IEC 2143/05
Key
w Mesh size
NOTE
The mesh size should comply with Table 2.
Figure E.22b – LPS air-termination on a sloped-roof structure
62305-3 © IEC:2006
– 189 –
A
IEC 2144/05
Key
A Test joint
NOTE
All dimensions should comply with the selected protection level according to Tables 1 and 2.
Figure E.22c – An example of LPS on a shed roof structure
62305-3 © IEC:2006
– 191 –
DC
DC
Conductor,either strip,
rod or metallic gutter
Cross section A
DC
DC
Ridge conductor fixed
below tile level (see detail)
DC
DC
Vertical air termination
or strike plate
Horizontal conductor
Cross section A
Concealed conductor
Vertical air termination (bare vertical rod) at short intervals, complying with the protective angle
or rolling sphere method (see Table 2)
DC
Down conductor
Figure E.22d – Air-termination and visually concealed conductors
for buildings less than 20 m high, with sloping roofs
Figure E.22 – Example of design of non-isolated LPS air-termination according to the
mesh method air-termination design
IEC 2145/05
62305-3 © IEC:2006
E.5.2.3
– 193 –
Air-terminations against flashes to the side on tall structures
In structures higher than 120 m, the topmost 20 % of lateral surfaces should be equipped with
air-termination systems.
NOTE If sensitive parts (e.g. electronic equipment) are present on the outside of the wall in the upper part of the
building, they should be protected by special air-termination measures, such as horizontal finials, mesh conductors
or equivalent.
E.5.2.4
Construction
E.5.2.4.1
General information
The maximum permissible temperature for a conductor will not be exceeded if the crosssection of the conductor conforms to Table 6.
A roof or wall constructed from combustible material should be protected from the dangerous
effect of lightning current heating the LPS conductors by using one or more of the following
measures:
–
reducing the temperature of the conductors by increasing the cross-section;
–
increasing the distance between the conductors and the roof covering (see also 5.2.4);
–
inserting a heat-protective layer between the conductors and the flammable material.
NOTE
Research has shown that it is advantageous for air-termination rods to have a blunt tip.
E.5.2.4.2
Non-isolated air-termination
Air-termination conductors and down-conductors should be interconnected by means of
conductors at the roof level to provide sufficient current distribution over the down-conductors.
Conductors on roofs and the connections of air-termination rods may be fixed to the roof
using either conductive or non-conductive spacers and fixtures. The conductors may also be
positioned on the surface of a wall if the wall is made of non-combustible material.
Recommended fixing centres for these conductors are shown in Table E.1.
Table E.1 – Suggested fixing centres
Fixing centres for
tape and stranded
conductors
mm
Fixing centres for
round solid conductors
Horizontal conductors on horizontal surfaces
500
1 000
Horizontal conductors on vertical surfaces
500
1 000
Vertical conductors from the ground to 20 m
1 000
1 000
Vertical conductors from 20 m and thereafter
500
1 000
Arrangement
NOTE 1
mm
This table does not apply to built-in type fixings which may require special consideration.
NOTE 2 Assessment of environmental conditions (i.e. expected wind load) should be undertaken and fixing
centres different from those recommended may be found to be necessary.
62305-3 © IEC:2006
– 195 –
On small houses and similar structures with a roof ridge, a roof conductor should be installed
on the roof ridge. If the structure is completely within the protected area provided by the roofridge conductor, at least two down-conductors should be routed over the gable edges at
opposite corners of the structure.
NOTE The distance between the two down-conductors, measured along the perimeter of the structure should not
exceed the distances stated in Table 4.
The gutters at the edge of the roof may be used as natural conductors provided that they
conform to 5.2.5.
Figures E.23a, E.23b and E.23c depict an example of the arrangement of the conductors on a
roof and down-conductors for a sloped roof structure.
62305-3 © IEC:2006
– 197 –
α
a
e
b
c
d
IEC 2146/05
IEC 2147/05
Figure E.23a − Installation of air-termination conductor
on the ridge of a sloped roof and a roof down-conductor
Figure E.23b − Installation of air-termination rod for
protection of chimney using the protective angle
air-termination design method
i
j
f
h
k
g
IEC 2148/05
Figure E.23c − Installation of a down-conductor
with connection to the gutter
IEC 2149/05
Figure E.23d − Installation of a test joint in
a down-conductor and bonding to a drain-pipe
Examples of suitable dimensions:
a 1m
b 0,15 m (not mandatory)
c 1m
d as close to the edge as possible
e 0,2 m
f
0,3 m
g 1m
h 0,05 m
i
0,3 m
j 1,5 m
k 0,5 m
α Protective angle according to Table 2
Figure E.23 – Some examples of details of an LPS on a structure with sloped tiled roofs
62305-3 © IEC:2006
– 199 –
In the case of long structures, additional conductors in accordance with Table 4 should be
connected to the air-termination conductors mounted on the roof ridge.
On buildings with large roof overhangs, the roof-ridge conductor should be extended to the
end of the ridge. On the gable edge of the roof a conductor should be connected from the
roof-ridge conductor to the down-conductor.
As far as is practicable, air-termination conductors, connecting conductors and downconductors should be installed in a straight route. On non-conducting roofs, the conductor
may be placed either under, or preferably over, the roof tiles. Although mounting it under the
tiles has the advantage of simplicity and less risk of corrosion, it is better, where adequate
fixing methods are available, to install it along the top of the tiles (i.e. externally) so reducing
the risk of damage to the tiles should the conductor receive a direct flash. Installing the
conductor above the tiles also simplifies inspection. Conductors placed below the tiles should
preferably be provided with short vertical finials which protrude above roof level and are
spaced not more than 10 m apart. Appropriate exposed metal plates may be also be used
(see Figure E.20d) provided they are spaced not more than 5 m apart.
On structures with flat roofs, the perimeter conductors should be installed as close to the
outer edges of the roof as practicable.
When the roof surface exceeds the mesh size stipulated in Table 2, additional air-termination
conductors should be installed.
Figures E.23a, E.23b and E.23c show examples of the construction details of fixtures for airtermination conductors on the sloped roof of a structure. Figure E.24 provides an example of
construction details for fixtures on a flat roof.
62305-3 © IEC:2006
– 201 –
1
2
3
4
5
a
6
7
8
IEC 2150/05
Key
a 500 mm to 1 000 mm, see Table F.1
1 Roof parapet
2 Flexible conductor
3 Joints
4 T-joints
5 Air-termination conductor fixture
6 LPS passing a watertight bushing
7 Steel girder
8 Joint
NOTE Metallic covering on the roof parapet is used as an air-termination conductor and is connected
to the steel girder used as a natural down-conductor of the LPS.
Figure E.24 – Construction of an LPS using natural components
on the roof of the structure
Figure E.25 shows the positioning of the external LPS on a structure with a flat roof made of
insulating material such as wood or bricks. The roof fixtures are within the space to be
protected. On high structures, a ring connected to all down-conductors is installed on the
facade. The distances between these ring conductors are given in Table 4. Ring conductors
below the level of the rolling sphere radius are needed as equipotentialization conductors.
62305-3 © IEC:2006
– 203 –
2
4
1
9
5
8
3
5
8
10
11
6
7
IEC 2151/05
Key
1
2
3
4
5
6
7
8
9
10
11
Air-termination rod
Horizontal air-termination conductor
Down-conductor
T-type joint
Cross-type joint
Test joint
B-type earthing arrangement, ring earth electrode
Equipotentialization ring conductor
Flat roof with roof fixture
Terminal for connecting the equipotentialization bar of the internal LPS
A-type earthing arrangement
NOTE An equipotentialization ring is applied. The distance between the down-conductors complies with the
requirements in Table 4.
Figure E.25 – Positioning of the external LPS on a structure made of insulating material
e.g. wood or bricks with a height up to 60 m with flat roof and with roof fixtures
62305-3 © IEC:2006
– 205 –
LPS conductors and rods should be mechanically secured so that they are capable of
withstanding stress due to wind or weather and work carried out on the roof surface.
Metal covering provided for mechanical protection of outer walls may be used as a natural
component of the air-termination, according to 5.2.5, if there is no risk of fire ignition by
melting metal. The combustibility depends on the type of material under the metal cladding.
The combustibility of the material employed should be confirmed by the contractor.
The roof sealing arrangement on metallic roofs, as with other types of roof, can be perforated
by a lightning flash. In such a case, water can penetrate and leak through the roof at a point
far from the striking point. If this possibility is to be avoided, an air-termination system should
be installed.
Light cupolas and smoke and heat outlet flaps are normally closed. The design for the
protection of such flaps should be discussed with the purchaser/owner of the building to
decide whether protection should be applicable for the flaps in the open, closed and all
intermediate positions.
Roof coverings of conductive sheet which do not conform to 5.2.5 may be used as airterminations where melting at the striking point of lightning can be accepted. If this is not
acceptable, the conductive roof sheeting should be protected by an air-termination system of
sufficient height (see Figure E.20 and Figure E.26).
r
a
a
IEC 2152/05
Key
r Radius of the rolling sphere, Table 2
a Air-termination conductors
NOTE
The rolling sphere should not touch any part of the metallic roof including the standing seams.
Figure E.26 – Construction of air-termination network on a roof with conductive
covering where puncturing of the covering is not acceptable
When insulating supports are used, the conditions for the separation distance to the
conductive sheet stipulated in 6.3, should be fulfilled.
When conductive supports are used, the connection to the roof-sheet should withstand partial
lightning current (see Figure E.26).
Figure E.24 shows an example of natural air-termination using a roof parapet as the airtermination conductor at the edge of the roof area.
Flush-mounted and protruding structures on the roof surface should be protected by means of
air-termination rods. Alternatively, extraneous metalwork should be bonded to the LPS unless
it conforms to 5.2.5.
62305-3 © IEC:2006
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Figure E.27 gives an example of the connection of air-termination with the natural downconductors in concrete.
2
4
3
9
1
5
6
4
6
7
10
8
IEC 2153/05
Key
1
2
3
4
5
6
7
8
9
10
Air-termination rod
Horizontal air-termination conductor
Down-conductor
T-type joint
Cross type joint
Connection to steel reinforcing rods (see E 4.3.3 and E.4.3.6)
Test joint
Type B earthing arrangement, ring earth electrode
Flat roof with roof fixtures
T-type joint – corrosion resistant
NOTE The steel reinforcement of the structure should comply with 4.3. All dimensions of the LPS should comply
with the selected protection level.
Figure E.27 – Construction of external LPS on a structure of steel-reinforced concrete
using the reinforcement of the outer walls as natural components
62305-3 © IEC:2006
E.5.2.4.2.1
– 209 –
Lightning protection for multi-storey car park roofs
For the protection of this type of structure, air-termination studs may be used. These studs
can be connected to the reinforcement steel of a concrete roof (see Figure E.28). In the case
of roofs where a connection to the reinforcement cannot be made, the roof conductors can be
laid in the seams of the carriageway slabs and air-termination studs can be located at the
mesh joints. The mesh width shall not exceed the value corresponding to the protection class
given in Table 2. In this case, the persons and vehicles on this parking area are not protected
against lightning.
1
2
3
IEC 2154/05
Key
1
2
3
Air-termination stud
Steel conductor connecting to several bars of the reinforcement steel
Steel reinforcement to concrete
Figure E.28 – Example of an air-termination stud used on car park roofs
If the topmost parking area is to be protected against direct lightning strikes, air-termination
rods and overhead air-termination wires should be employed.
For determination of the safety clearance, an approximation is given by the height of the airtermination conductors in Figure E.29.
62305-3 © IEC:2006
– 211 –
α
1
2
3
s
5
4
IEC 2155/05
Key
1 Protective cone
2 Metallic roof fixture
3 Horizontal air-termination conductor
4 Electric power installation line, preferably enclosed in a conductive shield
5 Electric equipment
s Separation distance according to 6.3
α Protective angle, see Table 2
NOTE
The height of the air-termination rod should comply with Table 2.
Figure E.29 – Air-termination rod used for protection of a metallic roof fixture with
electric power installations which are not bonded to the air-termination system
In the case of vertical conductors, the area which is possible to reach by hand should be
taken into account. The necessary safety clearance can be achieved either by provision of
barriers or by protective wiring.
Signs should be provided at the entrances drawing attention to the danger of lightning strikes
during thunderstorms.
The touch and step voltages may be disregarded if the roof is covered by a layer of asphalt of
at least 5 cm thickness. Additionally, the step voltages may be disregarded if the roof is
constructed of reinforced concrete with interconnected reinforcement steel with continuity
conforming to 4.3.
E.5.2.4.2.2
Flat-roofed, steel-reinforced concrete structures with roofs not
accessible to the public
On a flat roof not accessible to the public which incorporates an external air-termination
system, air-termination conductors should be installed as shown in Figure E.27. For the
equipotential ring conductor on the roof, the metal cladding on the roof parapet may be used
as shown in Figure E.24 and Figure E.30.
62305-3 © IEC:2006
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Key
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Corrosion-resistant joint
Flexible conductor
Metallic covering of the parapet
NOTE Special attention should be paid to the proper selection of materials and good design of joints and bridging
conductors to avoid corrosion.
Figure E.30 – Method of achieving electrical continuity on metallic parapet cladding
Figure E.27 shows a method of installing meshed conductors on a roof.
When temporary mechanical damage of the waterproof layer on the roof of a structure is
acceptable, the air-termination mesh covering the flat area of the roof may be replaced with
natural air-termination conductors consisting of steel reinforcement bars in concrete according
to 5.2.4 . An acceptable alternative is that the LPS air-termination conductors may be fixed
directly on the concrete roof.
In general, a lightning flash to the reinforcement of a concrete roof will damage the waterproof
layer. Rainwater may then cause corrosion of the steel-reinforcing rods leading to damage. If
reduction in the mechanical strength of concrete due to the corrosion is not permitted, an airtermination system should be installed and preferably bonded to the reinforcement steel,
preventing direct lightning flashes to the steel-reinforced concrete.
Metal covering that is provided for mechanical protection of outer walls may be used as a
natural component of the air-termination according to 5.2.5 if there is no risk of fire ignition by
melting metal.
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Roof coverings of conductive sheets not conforming to Table 3 may be used as airtermination conductors where melting at the point of lightning flashes can be tolerated. If not,
the conductive roof sheeting should be protected by an air-termination system of sufficient
height (see Figures E.20 and E.26). In this case, the rolling sphere method should be applied.
To conform to this method the mesh size has to be smaller and the supports higher than that
for an ordinary mesh air-termination system.
When insulating supports are used, the conditions for the separation distance to the
conductive sheet, stipulated in 6.3, should be fulfilled. When conductive supports are used,
the connection to the roof-sheet should withstand partial lightning current (see Figure E.29).
Figure E.24 shows an example of a natural air-termination using a roof parapet as the airtermination conductor at the edge of the roof area.
When it is acceptable for temporary damage to the facade to occur, and shattered parts of up
to 100 mm of broken concrete to fall down from the structure, 5.2 permits the ring conductor
on the roof to be replaced by a natural ring conductor consisting of steel reinforcement in
concrete.
Metal parts which do not satisfy the conditions of air-terminations stipulated in 5.2.5 may,
however, be used to connect the different lightning-current-carrying parts within the domain of
the roof area.
E.5.2.4.2.3
Provision of adequate structure shielding
The outer walls and roof of a structure may be used as an electromagnetic shield in order to
protect electrical and information-processing equipment within the structure (see IEC 623052, Annex B and IEC 62305-4).
Figure E.27 provides an example of a steel-reinforced concrete structure using the
interconnected reinforcing steel as down-conductors and as electromagnetic shielding of the
enclosed space. For more details see IEC 62305-4.
Within the domain of the air-termination system on the roof, all conductive parts with at least
one dimension larger than 1 m should be interconnected to form a mesh. The meshed shield
should be connected to the air-termination system at the roof edge and also at other points
within the roof area in accordance with 6.2.
Figures E.24 and E.30 show the construction of air-terminations on structures with conductive
skeletons using a roof parapet as a natural air-termination and the steel skeleton as natural
down-conductors.
In Figure E.30 an example is given of how to provide electrical continuity of natural
components in an LPS.
As a result of the reduced mesh size of steel structures compared with Table 2, the lightning
current is distributed over several parallel conductors, resulting in a low electromagnetic
impedance and consequently in accordance with 6.3, the separation distances are reduced
and the necessary separation distances between the installations and the LPS are much more
easily obtained.
In most structures the roof is the least shielded part of the structure. Therefore particular
attention should be paid to improve the shielding efficiency of roof constructions.
When no conductive structural elements are incorporated in the roof, shielding may be
improved by reducing the spacing of the roof conductors.
62305-3 © IEC:2006
E.5.2.4.2.4
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Protection of flush-mounted or protruding roof fixtures without
conductive installations
Air-termination rods for the protection of metal, flush-mounted roof fixtures or protruding roof
fixtures should be of such height that the fixture to be protected lies fully within the rolling
sphere protection space of the air-termination rod or is fully within the cone of the protective
angle in accordance with Table 2. The separation distance between the air-termination rods
and the roof fixtures should be such that the proximity condition stipulated in 6.3 is satisfied.
Figure E.29 shows an example of roof fixture protection by air-termination rods using the
protective angle air-termination design method. The value of the protective angle shall be
consistent with the protection level of the LPS stipulated in Table 2.
Metal roof fixtures, not protected by air-termination rods, do not require additional protection if
their dimensions do not exceed the following:
–
height above the roof level 0,3 m;
–
the total area of the superstructure 1,0 m 2 ;
–
the length of the superstructure 2,0 m.
Non-conductive roof fixtures which are not within the protected volume by air-termination rods
and which do not protrude by more than 0,5 m above the surface formed by the airtermination system do not require additional protection from air-termination conductors.
Conductive installations, such as electrical conductors or metallic pipes, which lead from
flush-mounted roof fixtures into the interior of the building can conduct a considerable portion
of the lightning current into the interior of the building. Where such conductive connections
exist, the protruding fixtures on the roof surface should be protected by air-termination
systems. If protection by means of an air-termination system is not possible or cost-effective,
insulated parts, with lengths corresponding to at least twice the specified separation distance,
can be installed in the conductive installations (e.g. compressed air pipes).
Chimneys of insulating material should be protected by means of air-termination rods or airtermination rings when they are not within the protective space of an air-termination system.
The air-termination rod on a chimney should be of such height that the complete chimney lies
within the protective space of the rod.
A lightning flash to a non-conductive chimney is possible when the chimney is not situated
within the protective space of an air-termination system, due to the fact that the inner surface
of the chimney is covered by a soot deposit possessing a conductivity such that, even in the
absence of rain, it is capable of conducting the current of a streamer discharge of great
length.
Figure E.23b shows the construction of an air-termination rod on a chimney made of
insulating bricks.
Metal flush-mounted roof fixtures should be bonded to the air-termination system when the
necessary clearance for conformity to the separation distance according to 6.3 cannot be
maintained.
E.5.2.4.2.5
Protection of roof fixtures enclosing electrical or informationprocessing equipment
All roof fixtures of insulating or conducting material, which contain electrical and/or
information-processing equipment, should lie within the protective space of the air-termination
system.
A direct flash into equipment installed inside the protective space of the air-termination
system is improbable.
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A direct flash into the roof fixture would lead not only to its destruction but would also cause
extended damage to the connected electrical and electronic equipment not only in the roof
fixtures, but also inside the building.
Roof fixtures on steel structures should also lie in the protective space of the air-termination
system. In this case air-termination conductors should be bonded not only to the airtermination system but also to the steel structure directly, if possible. When bonded to the
structure they need not conform to the separation distance.
The requirements for roof fixtures should also apply to fixtures installed on vertical surfaces to
which a lightning strike is possible, i.e. which can be touched by the rolling sphere.
Figure E.29 and Figure E.31 contain examples of air-termination constructions which protect
the roof fixtures of conducting and isolating material enclosing electrical installations.
Figure E.31 is only suitable if the separation distance s cannot be maintained.
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Key
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Air-termination conductor
Metallic cover
Bonding conductor
Horizontal air-termination conductor
Electric equipment
Electric power junction box with SPD
Bonding joint to the conductive elements of the structure
NOTE The enclosed electric equipment is bonded to the air-termination system and to the conductive elements of
the structure, complying with F.5.2.4.2.6, through the metallic cable shield withstanding a substantial part of the
lightning current.
Figure E.31 – Metallic roof fixture protected against direct lightning interception,
connected to air-termination system
62305-3 © IEC:2006
NOTE
level.
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If the fixtures need extra protection, SPDs on the active cables connected to it can be provided at roof
The required separation distance should be maintained not only in air but also for the path
through solid material (k m = 0,5).
E.5.2.4.2.6
Electrical installation protruding from the space to be protected
Antenna masts on the roof of a structure should be protected against direct lightning flashes
by installing the antenna mast in an already protected volume or by installing an isolated
external LPS.
If this is not possible, the antenna mast should be bonded to the air-termination system. Then
partial lightning currents will be treated inside the structure to be protected.
The antenna cable should enter the structure preferably at the common entrance for all
services or near the main LPS bonding bar. The antenna cable conductive sheath should be
bonded to the air-termination system on roof level and to the main bonding bar (see
Figure E.32).
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α
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IEC 2158/05
Key
1 Metallic mast
2 Horizontal air-termination conductor on the ridge of the roof
3 Joint between the roof down-conductor and the metallic antenna mast
4 Antenna cable
5 The main bonding bar; metallic shield on the antenna cable is connected to the bonding bar
6 Test joint
7 TV
8 Parallel routing of the antenna cable and the electric power cable
9 Electric power cable
10 Earth termination system
11 The main electric power distribution box with SPD
12 Foundation earth electrode
13 LPS conductor
l Length for separation distance
α Protective angle
NOTE
For small structures only two down-conductors may be sufficient, according to 5.3.3.
Figure E.32 – Example of construction of lightning protection of a house with a TV
antenna using the mast as an air-termination rod
Roof fixtures housing electrical equipment for which the separation distance cannot be
maintained, should be bonded to the air-termination system and to the conductive elements of
the roof fixtures and the conductive shield of its electrical equipment in accordance with
Table 9.
Figure E.31 is an example of the method of bonding a roof fixture with conductive parts to an
electrical installation and the air-termination of a structure.
62305-3 © IEC:2006
E.5.2.4.2.7
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Protection of conductive parts on the roof
Conductive items, such as those with insufficient wall thickness, which cannot withstand
lightning strikes and which are installed on roofs, and also conductive roof coverings or other
parts on structures which do not meet the requirements for natural air-termination systems
according to 5.2.5 and Table 3, and in which a lightning flash cannot be tolerated, should be
protected by air-termination conductors.
For the design of the lightning protection for conductive parts on the roof the rolling sphere
air-termination design method should be applied (see Figure E.33).
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s
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s
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IEC 2159/05
Key
1 Rolling sphere
2 Air-termination rod
3 Electric equipment
4 Down-conductor
5 Metallic vessel
r Radius of the rolling sphere, see Table 2
s Separation distance according to 6.3
Figure E.33 – Installation of lightning protection of metallic equipment on a roof against
a direct lightning flash
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Figure E.31 is an example of the design of an air-termination system protecting a conductive
roof fixture against a direct lightning flash when the separation distance s cannot be
maintained.
E.5.2.4.2.8
Protection of structures covered by soil
For structures incorporating a layer of soil on the roof and where people are not regularly
present, a normal LPS may be utilized. The air-termination system should be a meshed airtermination system on top of the soil, or a number of air-termination rods, connected by a
buried mesh, conforming to the rolling sphere or protective angle method. If this is not
possible, it should be recognized that a buried meshed air-termination system without rods or
finials will offer a reduced interception efficiency.
Structures with a roof layer of soil up to 0,50 m where people are regularly present, will need
a meshed air-termination system with meshes of 5 m × 5 m to prevent dangerous step
voltages. To protect the people on the ground from direct lightning flashes, air-termination
rods conforming to the rolling sphere method, may also be necessary. These rods can be
replaced by natural air-termination components, such as fences, lighting masts, etc. The
height of the air-termination systems shall take into account people’s height allowance of
2,5 m along with the necessary separation distances (see also Figure E.3).
If nothing of the kind is available, people should be made aware that during a thunderstorm
they may be exposed to a direct lightning flash.
For underground structures with a layer of soil over 0,5 m, measures are under consideration.
As long as there is no research available, it is adviseable to use the same measures as for
layers of soil up to 0,5 m.
For underground structures containing explosives materials, an additional LPS shall be
required. Such an additional LPS may be an isolated LPS over the structure. The earthing
systems of both protection measures should be interconnected.
E.5.2.5
Natural components
On structures with flat roofs, the metal covering of a roof parapet represents a typical natural
component of an LPS air-termination network. Such covering comprises extruded or bent
parts of aluminium, galvanized steel or copper in U-form which protect the upper surface of
the roof parapet against the influence of weather. The minimum thickness given in Table 3
shall be applied for such an application.
The air-termination conductors, conductors on the roof surface and the down-conductors
should be connected to the roof parapet covering.
Conductive bridging should be provided at the joints between sections of parapet covering
plates, unless there is good, reliable continuity between them.
Figure E.24 is an example of an air-termination construction using the conductive covering of
parapets as a natural air-termination conductor of the LPS.
Conductive parts, such as metal tanks, metal pipework and railings mounted on or extending
above a roof surface should be treated as natural components of an air-termination system
provided their wall thickness conforms to Table 3.
Vessels and pipework, which contain gas or liquids under high pressure or flammable gas or
liquids, should not be used as natural air-terminations. Where this cannot be avoided, the
heating effects of lightning current should be taken into account when designing the pipework.
62305-3 © IEC:2006
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Conductive parts above the roof surface such as metal tanks are often naturally connected to
equipment installed within the structure. In order to prevent conduction of the full lightning
current through the structure, it is necessary to provide a good connection between such
natural components of the LPS and the air-termination mesh.
Figure E.34 is an example, which show details of the bonding of conductive roof fixtures to
air-termination conductors.
2
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IEC 2160/05
Key
1
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4
Air-termination conductor fixing
Metallic pipe
Horizontal air-termination conductor
Steel reinforcement within concrete
NOTE 1 The steel pipe should comply with 5.2.5 and Table 6, the bonding conductor should comply with Table 6
and the reinforcement should comply with 4.3. The roof bonding should be watertight.
NOTE 2
In this particular case bonding is provided to the reinforcement of the reinforced concrete structure.
Figure E.34 – Connection of natural air-termination rod to air-termination conductor
Conductive parts above the roof surface such as metal tanks and steel reinforcing rods of
oncrete should be connected to the air-termination network.
When a direct lightning strike into the conductive part on the roof is not acceptable, the
conductive part shall be installed inside the protective space of an air-termination system.
Conductive coverings on facades and equivalent parts of structures where the risk of fire is
negligible should be treated in accordance with 5.2.5.
Figure E.35 shows an example of conductive bridging between metal facade plates
acceptable in those applications where the plates are to be used as natural down-conductors.
Two methods are presented: bridging by flexible metal strapping and bridging by means of
self-threading screws. Only bridging by flexible metal strapping may be used in applications
where the plates are used as natural lightning conductors. Bridging by means of selfthreading screws is only suitable for shielding purposes (protection against LEMP).
62305-3 © IEC:2006
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IEC 2161/05
Figure E.35a − Flexible metal strapping bridging
IEC 2162/05
Figure E.35b − Self tapping screw bridging
NOTE Electrically conducting bridging improves, in particular, the protection against LEMP. More information
concerning protection against LEMP can be found in IEC 62305-4.
Figure E.35 – Construction of the bridging between the segments
of the metallic façade plates
E.5.2.6
Isolated air-termination
Air-termination masts adjacent to structures or equipment to be protected are intended to
minimize the possibility of lightning strikes to structures within their zone of protection when
an isolated LPS is installed.
When more than one mast is installed, they may be interconnected by means of overhead
conductors and the proximity of the installations to the LPS should be in accordance with 6.3.
Overhead conductor connections between the masts extend the protected volume and also
distribute the lightning current between several down-conductor paths. The voltage drop along
the LPS and the electromagnetic interference in the space to be protected are therefore lower
than in the case when the overhead conductors are not present.
The strength of the electromagnetic field in the structure is reduced because of the greater
distance between the installations within the structure and the LPS. An isolated LPS may also
be applied to a structure of reinforced concrete, which will improve the electromagnetic
shielding even more. However, for tall structures the construction of an isolated LPS is not
practical.
62305-3 © IEC:2006
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Isolating air-termination systems made of stretched wires on insulated supports could be
suitable where a large number of extensive protruding fixtures on the roof surface are to be
protected. The insulation of the supports should be adequate for a voltage calculated from the
separation distance in accordance with 6.3.
E.5.3
E.5.3.1
Down-conductor systems
General
The choice of number and position of down-conductors should take into account the fact that,
if the lightning current is shared in several down-conductors, the risk of side flash and
electromagnetic disturbances inside the structure is reduced. It follows that, as far as
possible, the down-conductors should be uniformly placed along the perimeter of the structure
and with a symmetrical configuration.
The current sharing is improved not only by increasing the number of down-conductors but
also by equipotential interconnecting rings.
Down-conductors should be placed as far as possible away from internal circuits and metallic
parts in order to avoid the need for equipotential bonding with the LPS.
It should be remembered that
–
the down-conductors should be as short as possible (to keep inductance as small as
possible),
–
the typical distance between down-conductors is shown in Table 4,
–
the geometry of down-conductors and equipotential interconnecting rings has an influence
on the value of the separation distance (see 6.3),
–
in cantilevered structures the separation distance should also be evaluated with reference
to the risk of side-flashing to persons (see E.4.2.4.2).
If it is not possible to place down-conductors at a side, or part of a side, of the building
because of practical or architectural constraints, the down-conductors that ought to be on that
side should be placed as extra compensating down-conductors at the other sides. The
distances between these down-conductors should not be less than one-third of the distances
in Table 4.
A variation in spacing of the down-conductors of ±20 % is acceptable as long as the mean
spacing conforms to Table 4.
In closed courtyards with more than 30 m perimeter, down-conductors have to be installed.
Typical values of the distance between down-conductors are given in Table 4.
E.5.3.2
Number of down-conductors for isolated LPS
No additional information.
E.5.3.3
Number of down-conductors for non-isolated LPS
No additional information.
E.5.3.4
E.5.3.4.1
Construction
General information
External down-conductors should be installed between the air-termination system and the
earth-termination system. Wherever natural components are available they can be used as
down-conductor.
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If the separation distance between down-conductors and the internal installations, calculated
on the basis of the down-conductor spacing according to Table 4, is too large, the number of
down-conductors should be increased to meet the required separation distance.
Air-termination systems, down-conductor systems and earth-termination systems should be
harmonized to produce the shortest possible path for the lightning current.
Down-conductors should preferably be connected to junctions of the air-termination system
network and routed vertically to the junctions of the earth-termination system network.
If it is not possible to make a straight connection because of large roof overhangs etc. the
connection of the air-termination system and the down-conductor should be a dedicated one
and not through natural components like rain gutters etc.
Figure E.36 is an example of an external LPS for a structure with different levels of roof
construction and Figure E.25 is an example of the external LPS design for a 60 m high
structure with a flat roof with roof fixtures.
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IEC 2163/05
Key
1
Horizontal air-termination conductor
2
Down-conductor
3
T-type joint – corrosion resistant
4
Test joint
5
Type B earthing arrangement, ring earth electrode
6
T-type joint on the ridge of the roof
7
Mesh size
NOTE The distance between the down-conductors should comply with 5.2, 5.3 and Table 4 .
Figure E.36 – Installation of external LPS on a structure of isolating material with
different roof levels
In structures without extensive continuous conductive parts, the lightning current only flows
through the ordinary down-conductor system of the LPS. For this reason the geometry of
down-conductors determines the electromagnetic fields within the interior of the structure (see
Figure E.37).
62305-3 © IEC:2006
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IEC 2164/05
Figure E.37b
Figure E.37a
Figure E.37c
IEC 2166/05
Figure E.37d
IEC 2165/05
IEC 2167/05
IEC 2168/05
Figure E.37e
Natural components of the LPS, e.g. gutters
LPS conductors
Test Joint
Joint
NOTE The distance between the down-conductors and the mesh size should comply with the selected lightning
protection level according to Tables 2 and 4.
Figure E.37 – Examples of geometry of LPS conductors
62305-3 © IEC:2006
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When the number of down-conductors is increased, the separation distance can be reduced
according to the coefficient k c (see 6.3).
According to 5.3.3, at least two down-conductors should be used on a structure (see
Figures E.38 and E.36).
s
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IEC 2169/05
Key
1
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Electric equipment
Electric conductors
LPS conductors
Main electric power distribution box with SPD
Test joint
Earth-termination system
Electric power cable
Foundation earth electrode
Separation distance according to 6.3
Length for the evaluation of the separation distance s
NOTE The example illustrates the problems introduced by electric power or other conductive installations in the
roof space of a building.
Figure E.38 – Construction of an LPS using only two down-conductors
and foundation earth electrodes
For large structures, such as high-rise apartment buildings and, in particular, industrial and
administrative structures, which are often designed as steel skeletons or steel and concrete
skeleton structures, or which use steel-reinforced concrete, the conductive structure
components may be used as natural down-conductors.
The total impedance of the LPS for such structures is fairly low and they afford a very efficient
lightning protection for inner installations. It is particularly advantageous to use conductive
wall surfaces as down-conductors. Such conductive wall surfaces might be: reinforced
concrete walls, metallic sheet facade surfaces and facades of prefabricated concrete
elements, provided they are connected and interlinked according to 5.3.5.
62305-3 © IEC:2006
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Figure E.4 provides a detailed description of the proper construction of an LPS using natural
LPS components such as interconnected steel.
Use of natural components containing structural steel reduces the voltage drop between the
air-termination system and the earth-termination system and the electromagnetic interference
caused by lightning current within the structure.
If the air-termination system is connected to the conductive parts of the columns within the
structure complex and to the equipotential bonding at ground level, a portion of the lightning
current flows through these internal down-conductors. The magnetic field of this partial
lightning current influences neighbouring equipment and has to be considered in the design of
the internal LPS and electrical and electronic installations. The magnitude of these partial
currents depends on the dimensions of the structure and on the number of columns, assuming
the current waveform follows the waveform of the lightning current.
If the air-termination system is insulated from the internal columns no current flows through
the columns within the structure complex, provided the insulation does not break down. If the
insulation breaks down at an unpredicted point, a larger partial current may flow through a
particular column or group of columns. The current steepness may increase due to the
reduced virtual duration of the wave front caused by the breakdown and the neighbouring
equipment is affected to a greater extent than it would be in the case of controlled bonding of
columns to the LPS of the structure.
Figure E.10 is an example of the construction of internal down-conductors in a large steelreinforced concrete structure used for industrial purposes. The electromagnetic environment
near to the inner columns shall be considered when planning the internal LPS.
E.5.3.4.2
Non-isolated down-conductors
In structures with extensive conductive parts in the outer walls, the air-termination conductors
and the earth-termination system should be connected to the conductive parts of the structure
at a number of points. This will reduce the separation distance according to 6.3.
As a result of these connections the conductive parts of a structure are used as downconductors and also as equipotential bonding bars.
In large, flat structures (typically industrial structures, exhibition halls, etc.) with dimensions
over four times the spacing of the down-conductors, extra internal down-conductors should be
provided approximately every 40 m, wherever possible.
All internal columns and all internal partition walls with conductive parts, such as steel
reinforcing rods, which do not fulfil the separation distance conditions, should be connected
with the air-termination system and with the earth-termination system at suitable points.
Figure E.10 shows the LPS of a large structure with internal columns made of steel-reinforced
concrete. To avoid dangerous sparking between different conductive parts of the structure,
the reinforcement of the columns is connected to the air-termination system and to the earthtermination system. As a result, a portion of the lightning current will flow through these
internal down-conductors. However, the current is divided among numerous down-conductors
and has approximately the same waveform as the current in the lightning stroke. The
steepness of the wavefront, however, is reduced. If these connections are not made and a
flashover occurs, only one or a few of these internal down-conductors may carry the current.
62305-3 © IEC:2006
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The waveform of the flashover current will be considerably steeper than the lightning current,
so the voltage induced in neighbouring circuit loops will be considerably increased.
For such structures, it is particularly important that before commencing the design of the
structure, the structure’s design as well as the design of the LPS should be harmonized so
that conductive parts of the structure can be utilized for lightning protection. By means of wellcoordinated design, a highly effective LPS is achieved at minimum cost.
Lightning protection of space and persons below an overhanging upper storey, such as a
cantilevered upper floor, should be designed according to 4.2.4.2 and Figure E.3.
E.5.3.4.3
Isolated down-conductors
If, due to architectural considerations, the down-conductors cannot be surface mounted, they
should be installed in open slits in the brickwork. In this case, consideration should be given
to maintaining the separation distance, as given in 6.3, between the down-conductor and any
metal parts inside the structure.
Direct installation within the external plaster is not recommended since the plaster may be
damaged as a result of thermal expansion. Moreover, the plaster may be discoloured as a
result of chemical reaction. Damage to the plaster is particularly likely as a result of
temperature rise and mechanical forces exerted by lightning current; PVC-covered conductors
prevent staining.
E.5.3.5
Natural components
The use of natural down-conductors to maximize the total number of parallel current
conductors is recommended as this minimizes the voltage drop in down-conductor systems
and reduces the electromagnetic interference within the structure. However, it should be
ensured that such down-conductors are electrically continuous along the entire path between
the air-termination system and the earth-termination system.
The steel reinforcement in concrete walls should be used as a natural component of the LPS
as illustrated in Figure E.27.
Steel reinforcement of newly erected structures should be specified in accordance with E.4.3.
If electrical continuity of the natural down-conductors cannot be guaranteed, conventional
down-conductors should be installed.
For structures with low protection requirements, a metallic rain-pipe which satisfies the
conditions for natural down-conductors according to 5.3.5, may be used as a down-conductor.
Figures E.23a, E.23b and E.23c show examples of fixing the conductors on the roof and the
down-conductors including appropriate geometrical dimensions, and Figures E.23c and E.23d
show the connections of the down-conductor to the metallic rain-pipe, the conductive gutters
and the earth-termination conductor.
The reinforcing rods of walls or concrete columns and steel structural frames may be used as
natural down-conductors.
A metal facade or a facade covering on a structure may be used as a natural down-conductor
conforming to 5.3.5.
Figure E.8 shows construction of a natural down-conductor system using metal facade
elements and steel reinforcing in the concrete walls as the equipotentialization reference
plane to which the equipotentialization bars of the internal LPS are connected.
62305-3 © IEC:2006
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Connections should be provided at the top of the wallcovering, to the air-termination system
and at the bottom of the earth-termination system and to the reinforcing rods of the concrete
walls, if applicable.
The distribution of current in such metal facades is more consistent than in reinforced
concrete walls. Sheet metal facades comprise individual panels generally of trapezoidal
cross-section with a width between 0,6 m and 1,0 m and a length corresponding to the height
of the structure. In the case of high-rise structures, the panel length does not correspond to
the structure height due to transport problems. The whole facade then comprises a number of
sections mounted one above the other.
For a metal facade, the maximum thermal expansion should be calculated as the difference in
length produced by a maximum temperature of the metal facade in sunlight of approximately
+80 °C and a minimum temperature of –20 °C .
The temperature difference of 100 °C corresponds to a thermal expansion of 0,24 % for
aluminium and 0,11 % for steel.
Thermal expansion of the panels results in movement of the panels with respect to the next
section or to the fixtures.
Metal connections, such as those depicted in Figure E.35, encourage uniform current
distribution in metal facades and thus reduce the influence of the electromagnetic field inside
the structure.
A metal facade produces maximum electromagnetic shielding when it is electrically
interconnected over its whole area.
High electromagnetic shielding efficiency of a structure is obtained when permanent bonding
of adjacent metal facades is carried out at sufficiently small intervals.
Symmetry of current distribution relates directly to the number of connections.
If stringent requirements with respect to shield attenuation exist and continuous strip windows
are incorporated in such a facade, the continuous strip windows should be bridged by means
of conductors at small intervals. This may be done by means of metal window frames. The
metal facade should be connected to the window frame at short intervals. Generally, each
ridge is connected to the horizontal tie-beam of the window frame at intervals not exceeding
the spacing of the vertical members of the window construction. Bends and detours should
always be avoided (see Figure E.9).
Metal facades comprised of relatively small elements which are not interconnected cannot be
used as a natural down-conductor system or for electromagnetic shielding.
More information on the protection of electrical installations and electronics in structures is
available in IEC 62305-4.
E.5.3.6
Test joint
Test joints facilitate measurements of the earth resistance of earth-termination system.
Test joints conforming to 5.3.6, should be installed in the connection of the down-conductors
to the earth-termination system. These joints facilitate the determination by measurement that
an adequate number of connections to the earth-termination system still exists. It is thus
possible to validate the existence of continuous connections between the test joint and the
air-termination system or the next bonding bar. On tall structures, ring-conductors are
connected to the down-conductors, which may be installed in the wall and invisible to the eye;
their existence may only be confirmed by electric measurement.
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Figure E.39a through Figure E.39d show examples of test joint designs, which may be
installed on the inner or outer wall of a structure or in a test box in the earth outside the
structure (see Figure E.39b). To make the continuity measurements possible, some
conductors may have to have insulating sheaths on critical sections.
9
6
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8
7
7
IEC 2170/05
IEC 2171/05
Figure E.39a
Figure E.39b
1
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4
5
7
IEC 2172/05
IEC 2173/05
Figure E.39c
Figure E.39d
Alternative 1 – Test joint on wall
Alternative 2 – Test joint in the floor
1
Down-conductor
1
Down-conductor
2
Type B earth electrode, if applicable
2
Type A earth electrode, if applicable
3
Type A earth electrode, if applicable
3
Bonding bar of the internal LPS
4
Foundation earth electrode
4
Type B - Ring earth electrode
5
Bonding to the internal LPS
5
Type B - Ring earth electrode
6
Test joint on the wall
6
Test joint in the floor
7
Corrosion-resistant T-joint in soil
7
Corrosion-resistant T- joint in soil
8
Corrosion-resistant joint in soil
8
Corrosion-resistant joint in soil
9
Joint between lightning conductor and a steel girder
9
Joint between lightning conductor and a steel girder
NOTE 1 The test joint detailed in Figure F.39d should be installed on the inner or outer wall of a structure or in a
test box in the earth outside the structure.
NOTE 2 To make the loop resistance measurements possible, some of the connecting conductors should have
insulating sheaths along critical sections.
Figure E.39 – Examples of connection of earth termination to the LPS of structures
using natural down-conductors (girders) and detail of a test joint
62305-3 © IEC:2006
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If it makes sense (e.g. in the case of earthing connections to steel columns via connecting
conductors), connections from natural down-conductors to earth-termination electrodes may
be provided with insulated conductor segments and testing joints. Special reference earth
electrodes shall be installed to facilitate monitoring of the earth-termination system of an LPS.
E.5.4
E.5.4.1
Earth-termination system
General
The LPS designer and the LPS installer should select suitable types of earth electrodes and
should locate them at safe distances from entrances and exits of a structure and from the
external conductive parts in the soil. The LPS designer and the LPS installer should make
special provisions for protection against dangerous step voltages in the vicinity of the earthtermination networks if they are installed in areas accessible to the public (see Clause 8).
The embedded depth and the type of the earth electrodes should be such as to minimize the
effects of corrosion, soil drying and freezing and thereby stabilize the equivalent earth
resistance.
It is recommended that the first metre of a vertical earth electrode should not be regarded as
being effective under frost conditions.
Deep-driven earth electrodes can be effective in special cases where soil resistivity
decreases with depth and where substrata of low resistivity occur at depths greater than those
to which rod electrodes are normally driven.
When the metallic reinforcement of concrete is used as an earth electrode, special care
should be exercised at the interconnections to prevent mechanical splitting of the concrete.
If the metal reinforcement is also used for the protective earth, the most severe measure in
respect of thickness of the rods and the connection should be chosen. In this case, larger
sizes of reinforcement bars could be considered. The need for short and straight connections
for the lightning protection earthing should be recognized at all times.
NOTE In the case of pre-stressed concrete, consideration should be given to the consequences of the passage of
lightning discharge currents, which may produce unacceptable mechanical stresses.
E.5.4.2
E.5.4.2.1
Types of earth electrode arrangements
Type A arrangement
The type A earth-termination system is suitable for low structures (for example family
houses), existing structures or an LPS with rods or stretched wires or for an isolated LPS.
This type of arrangement comprises horizontal or vertical earth electrodes connected to each
down-conductor.
Where there is a ring conductor, which interconnects the down-conductors, in contact with the
soil the earth electrode arrangement is still classified as type A if the ring conductor is in
contact with the soil for less than 80 % of its length.
In a type A arrangement the minimum number of earth electrodes should be two.
62305-3 © IEC:2006
E.5.4.2.2
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Type B arrangement
The type B earth-termination system is preferred for meshed air-termination systems and for
LPS with several down-conductors.
This type of arrangement comprises either a ring earth electrode external to the structure in
contact with the soil for at least 80 % of its total length or a foundation earth electrode.
For bare solid rock, only the type B earthing arrangement is recommended.
E.5.4.3
E.5.4.3.1
Construction
General
Earth-termination systems should perform the following tasks:
–
conduction of the lightning current into the earth;
–
equipotential bonding between the down-conductors;
–
potential control in the vicinity of conductive building walls.
The foundation earth electrodes and the type B ring-type earth electrodes meet all these
requirements. Type A radial earth electrodes or deep-driven vertical earth electrodes do not
meet these requirements with respect to equipotential bonding and potential control.
The structure foundations of interconnected steel-reinforced concrete should be used as
foundation earth electrodes. They exhibit very low earthing resistance and perform an
excellent equipotentialization reference. When this is not possible, an earth-termination
system, preferably a type B ring earth electrode, should be installed around the structure.
E.5.4.3.2
Foundation earth electrodes
A foundation earth electrode, which conforms to 5.4.4, comprises conductors, which are
installed in the foundation of the structure below ground. The length of additional earth
electrodes should be determined using the diagram in Figure 2.
Foundation earth electrodes are installed in concrete. They have the advantage that, if the
concrete is of adequate construction and covers the foundation earth electrode by at least
50 mm, they are reasonably protected against corrosion. It should also be remembered that
reinforcing steel rods in concrete generate the same magnitude of galvanic potential as
copper conductors in soil. This offers a good engineering solution to the design of earthtermination systems for reinforced concrete structures (see E.4.3).
Metals used for earth electrodes should conform to the materials listed in Table 7, and the
behaviour of the metal with respect to corrosion in the soil should always be taken into
account. Some guidance is given in 5.6. When guidance for particular soils is not available,
the experience with earth-termination systems in neighbouring plants, with soil exhibiting
similar chemical properties and consistency, should be ascertained. When the trenches for
earth electrodes are refilled, care should be taken that no fly ash, lumps of coal or building
rubble is in direct contact with the earth electrode.
A further problem arises from electrochemical corrosion due to galvanic currents. Steel in
concrete has approximately the same galvanic potential in the electrochemical series as
copper in soil. Therefore, when steel in concrete is connected to steel in soil, a driving
galvanic voltage of approximately 1 V causes a corrosion current to flow through the soil and
the wet concrete and dissolve steel in soil.
Earth electrodes in soil should use copper or stainless steel conductors where these are
connected to steel in concrete.
62305-3 © IEC:2006
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At the perimeter of a structure, a metal conductor, in accordance with Table 7, or a galvanized
steel strip, should be installed in the strip foundation and be taken upwards with connection
leads to the designated terminal points of the lightning down-conductor test joints.
Upward routing of the conductors connected to the down-conductors can be performed on the
brickwork, within the plaster or within the wall. The steel connection leads installed within the
wall may penetrate the asphalt-saturated paper normally used between the foundation and the
brick wall. Piercing of the humidity barrier at this point generally presents no problem.
The water-insulating layer often inserted below the structure foundation to reduce the
humidity in basement floors provides consistent electrical insulation. The earth electrode
should be installed under the foundation in the sub-concrete. An agreement should be
obtained with the builder for the design of the earth-termination system.
Where the groundwater level is high, the foundation of the structure should be isolated from
subsoil water. A sealing waterproof layer should be applied to the outer surface of the
foundation, which also provides electrical insulation. The usual practice in establishing such a
waterproof foundation, is to pour a clean layer of concrete approximately 10 cm to 15 cm in
depth on the bottom of the foundation pit, onto which the isolation, and later the concrete
foundation, is laid.
A foundation earth electrode consisting of a network of mesh size not exceeding 10 m shall
be installed in the clean concrete layer at the bottom of the foundation pit.
A conductor in accordance with Table 7 shall connect the meshed earth-termination with the
reinforcement in the foundation, the ring earth electrodes, and the down-conductors external
to the humidity barrier. Where permitted, pressure-waterproof bushings may be used to
penetrate the insulation.
When penetration of the conductor through the isolation layer is not permitted by the building
contractor, connections should be made to the earth termination outside the structure.
Figure E.40 shows three different examples of how to install foundation earth electrodes on a
structure with waterproofed foundations to avoid piercing of the humidity barrier.
62305-3 © IEC:2006
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1
1
3
2
2
3
7
7
4
5
6
6
IEC 2174/05
Figure E.40a – Isolated foundation with foundation earth electrode
in the non-reinforced concrete layer below the bitumen insulation
Figure E.40b – Isolated foundation with earth-termination
conductor partly passing through the soil
9
8
3
7
6
10
IEC 2176/05
Figure E.40c – Connecting conductor from the foundation earth electrode
to the bonding bar passing the bitumen insulating layer
Key
1
2
3
4
5
6
7
8
9
10
Down-conductor
Test joint
Bonding conductor to the internal LPS
Non-reinforced layer of concrete
Connecting conductor of the LPS
Foundation earth electrode
Bitumen insulation, watertight insulating layer
Connecting conductor between steel reinforcement and the test joint
Steel reinforcement in concrete
Puncturing of the watertight bitumen layer
NOTE
IEC 2175/05
Permission from the structure constructor is necessary.
Figure E.40 – Construction of foundation earth ring for structures
of different foundation design
62305-3 © IEC:2006
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Several solutions of an adequate connection of the earth termination on structures with
isolated foundation are also illustrated.
Figures E.40a and E.40b show connections external to the insulation, so that the insulation is
not damaged; Figure E.40c shows a bushing through the insulation.
E.5.4.3.3
Type A – Radial and vertical earth electrodes
Radial earth electrodes should be connected to the lower ends of the down-conductors by
using test joints. Radial earth electrodes may be terminated by vertical earth electrodes if
appropriate.
Each down-conductor should be provided with an earth electrode.
Figure E.41 shows a type A earth electrode where a lightning conductor in accordance with
Table 7 is pushed into the soil using special driving rods. This earthing technique has several
practical advantages and avoids the use of clamps and joints in the soil. Sloped or vertical
earth electrodes are generally hammered in.
62305-3 © IEC:2006
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2
1
3
4
5
IEC 2177/05
Key
1
2
3
4
5
Short upper-most driving rod
Earthing conductor
Soil
Short driving rods
Driving steel dart
NOTE 1 A continuous wire conductor is driven into the soil by means of short driving rods. The electrical
continuity of the earth electrode conductor is of great advantage; using this technique, no joints are introduced into
the earth electrode conductor. Short driving rod segments are also easy to handle.
NOTE 2
The short upper-most driving rod may be removed.
NOTE 3
The uppermost part of the earthing conductor may have an insulating jacket.
Figure E.41a – Example of a type A earthing arrangement with a vertical conductor type electrode
5
4
1
3
2
1
IEC 2178/05
Key
1
2
3
4
5
Extensible earth rod
Rod coupling
Soil
Conductor to rod clamp
Earthing conductor
Figure E.41b – Example of a type A earthing arrangement with a vertical rod type electrode
Figure E.41 – Examples of two vertical electrodes in type A earthing arrangement
62305-3 © IEC:2006
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There are also other types of vertical electrodes. It is essential to ensure a permanent
conducting connection along the whole length of the electrode during the service life of the
LPS.
During installation it is advantageous to measure the earthing resistance regularly. The
driving may be interrupted as soon as the earthing resistance stops decreasing. Additional
electrodes can then be installed in more suitable locations.
The earth electrode should have sufficient separation from existing cables and metal pipes in
the earth, and due allowance should be made for the earth electrode departing from its
intended position during driving. The separation distance depends on the electrical impulse
strength and resistivity of the soil and the current in the electrode.
In the type A arrangement, vertical earth electrodes are more cost-effective and give more
stable earthing resistances in most soils than horizontal electrodes.
In some cases it may be necessary to install the earth electrodes inside the structure, for
example in a basement or cellar.
NOTE Special care should be taken to control step voltages by taking equipotentialization measures according to
Clause 8.
If there is a danger of an increase in resistance near to the surface (e.g. through drying out),
it is often necessary to employ deep-driven earth electrodes of greater length.
Radial earth electrodes should be installed at a depth of 0,5 m or deeper. A deeper electrode
ensures that in countries in which low temperatures occur during the winter, the earth
electrode is not situated in frozen soil (which exhibits extremely low conductivity). An
additional benefit is that deeper earth electrodes give a reduction of the potential differences
at the earth surface and thus lower step voltages reducing the danger to living creatures on
the earth surface. Vertical electrodes are preferred to achieve a seasonally-stable earthing
resistance.
When the type A earthing arrangement is provided, the necessary potential equalization for all
electrodes is achieved by means of equipotential bonding conductors and bonding bars
preferably outside the structure.
E.5.4.3.4
Type B – Ring earth electrodes
For structures using insulating material such as brickwork or wood with no steel-reinforced
foundation, a type B earth termination should be installed conforming to 5.4.2.2.
In order to reduce the equivalent earth resistance, the type B earthing arrangement may be
improved, if necessary, by adding vertical earth electrodes, or radial earth electrodes
conforming to 5.4.2.2. Figure 2 gives the requirements regarding the minimum length of earth
electrodes.
The clearance and depth for a type B earth electrode, as mentioned in 5.4.3, are optimal in
normal soil conditions for the protection of persons in the vicinity of the structure. In countries
with low winter temperatures, the appropriate depth of earth electrodes should be considered.
Type B earth electrodes also perform the function of potential equalization between the downconductors at ground level, since the various down-conductors give different potentials due to
the unequal distribution of lightning currents due to variations in the earth resistance. The
different potentials result in a flow of equalizing currents through the ring earth electrode, so
that the maximum rise in potential is reduced and the equipotential bonding systems
connected to it within the structure are brought to approximately the same potential.
62305-3 © IEC:2006
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Where structures belonging to different owners are built close to each other, it is often not
possible to install a ring earth electrode that will fully surround the structure. In this case the
efficiency of the earth-termination system is somewhat reduced, since the conductor ring acts
partly as a type B electrode, partly as a foundation earth and partly as an equipotential
bonding conductor.
Where large numbers of people frequently assemble in an area adjacent to the structure to be
protected, further potential control for such areas should be provided. More ring earth
electrodes should be installed at distances of approximately 3 m from the first and subsequent
ring conductors. Ring electrodes further from the structure should be installed more deeply
below the surface i.e. those at 4 m from the structure at a depth of 1 m, those at 7 m from the
structure at a depth of 1,5 m and those at 10 m from the structure at a depth of 2 m. These
ring earth electrodes should be connected to the first ring conductor by means of radial
conductors.
When the area adjacent to the structure is covered with a 50 mm thick slab of asphalt of low
conductivity, sufficient protection is provided for people making use of the area.
E.5.4.3.5
Earth electrodes in rocky soil
During construction, a foundation earth electrode should be built into the concrete foundation.
Even where a foundation earth electrode has a reduced earthing effect in rocky soil, it still
acts as an equipotential bonding conductor.
At the test joints, additional earth electrodes should be connected to the down-conductors and
foundation earth electrodes.
Where a foundation earth electrode is not provided, a type B arrangement (a ring earth
electrode) should be used instead. If the earth electrode cannot be installed in the soil and
has to be mounted on the surface, it should be protected against mechanical damage.
Radial earth electrodes lying on or near the earth surface should be covered by stones or
embedded in concrete for mechanical protection.
When the structure is situated close to a road, if possible, a ring earth electrode should be
laid beneath the road. However, where this is not possible over the whole length of the
exposed road segment, such equipotential control (typically a type A arrangement) should be
provided at least in the vicinity of the down-conductors.
For potential control in certain special cases, a decision should be made as to whether to
install a further partial ring in the vicinity of the structure entrance, or to artificially increase
the resistivity of the surface layer of the soil.
E.5.4.3.6
Earth-termination systems in large areas
An industrial plant typically comprises a number of associated structures, between which a
large number of power and signal cables are installed.
The earth-termination systems of such structures are very important for the protection of the
electrical system. A low impedance earth system reduces the potential difference between the
structures and so reduces the interference injected into the electrical links.
A low earth impedance can be achieved by providing the structure with foundation earth
electrodes and additional type B and type A earth arrangements conforming to 5.4.
62305-3 © IEC:2006
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Interconnections between the earth electrodes, the foundation earth electrodes and the downconductors should be installed at the test joints. Some of the test joints should also be
connected to the equipotential bars of the internal LPS.
Internal down-conductors, or internal structural parts used as down–conductors, should be
connected to an earth electrode and the reinforcement steel of the floor to avoid step and
touch voltages. If internal down-conductors are near expansion joints in the concrete, these
joints should be bridged as near to the internal down-conductor as possible.
The lower part of an exposed down-conductor should be isolated by PVC tubing with a
thickness of at least 3 mm or with equivalent insulation.
In order to reduce the probability of direct lightning flashes to cable routes in the ground, an
earthing conductor and, in the case of wider cable routes, a number of earthing conductors
should be installed above the cable routes.
By interconnecting the earths of a number of structures, a meshed earthing system is
obtained as shown in Figure E.42.
62305-3 © IEC:2006
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3
2
1
4
1
IEC 2179/05
Key
1 Building with meshed network of the reinforcement
2 Tower inside the plant
3 Stand-alone equipment
4 Cable trenches
NOTE This system gives a low impedance between buildings and has significant EMC advantages. The size of
the meshes next to buildings and other objects may be in the order of 20 m × 20 m. Beyond a 30 m distance they
may be enlarged to the order of 40 m × 40 m.
Figure E.42 – Meshed earth termination system of a plant
Figure E.42 shows the design of a meshed earth electrode network, including cable trenches,
between associated structures of lightning-protected buildings. This will give a low impedance
between buildings and has significant LEMP protection advantages.
62305-3 © IEC:2006
E.5.5
– 269 –
Components
No additional information.
NOTE
Distances between fixings are given in Table E.1.
E.5.6
E.5.6.1
Materials and dimensions
Mechanical design
The lightning protection designer shall consult with the persons responsible for the structure,
on mechanical design matters following the completion of the electrical design.
Aesthetic considerations are particularly important as well as the correct selection of materials
to limit the risk of corrosion.
The minimum size of lightning protection components for the various parts of the LPS are
listed in Tables 3, 6, 7, 8 and 9.
The materials used for the LPS components are listed in Table 5.
NOTE Components such as clamps and rods selected in accordance with the EN 50164 series may be considered
adequate.
The LPS designer and the LPS installer should verify the fitness of purpose of the materials
used. This can be achieved, for example, by requiring test certificates and reports from the
manufacturer, demonstrating that materials have successfully passed quality tests.
The LPS designer and the LPS installer should specify conductor fasteners and fixtures which
will withstand the electrodynamic forces of lightning current in the conductors and also allow
for the expansion and contraction of conductors due to the relevant temperature rise.
Connections between sheet metal panels should be compatible with the panel material,
represent a minimum contact surface area of 50 mm 2 and be capable of withstanding the
electrodynamic forces of a lightning current and the corrosion threats of the environment.
When excessive temperature rise is a concern for the surface to which the components are to
be attached because it is flammable or has a low melting point, either larger conductor crosssections should be specified, or other safety precautions should be considered, such as the
use of stand-off fittings and the insertion of fire-resistant layers.
The LPS designer should identify all corrosion problem areas and specify appropriate
measures to be taken.
The corrosion effects on the LPS may be reduced either by increases in material size, using
corrosion-resistant components or by taking other corrosion protection measures.
E.5.6.2
E.5.6.2.1
Selection of materials
Materials
LPS materials and conditions of use are listed in Table 5.
Dimensions of LPS conductors, including air-termination conductors, down-conductors and
earth-termination conductors, for different materials such as copper, aluminium and steel are
given in Tables 6 and 7.
62305-3 © IEC:2006
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Minimum thickness of metal sheets, metal pipes and containers used as natural airtermination components are listed in Table 3, and minimum dimensions for bonding
conductors are given in Tables 8 and 9.
E.5.6.2.2
Protection against corrosion
The LPS should be constructed of corrosion-resistant materials such as copper, aluminium,
stainless steel and galvanized steel. The material of the air-termination rods and airtermination wires should be electrochemically compatible with the material of the connection
elements and the mounting elements, and it should have a good corrosion resistance to a
corrosive atmosphere or moisture.
Connections between different materials should be avoided, otherwise they are to be
protected.
Copper parts should never be installed above galvanized or aluminium parts unless those
parts are provided with protection against corrosion.
Extremely fine particles are shed by copper parts which result in severe corrosive damage to
galvanized parts even where the copper and galvanized parts are not in direct contact.
Aluminium conductors should not be directly attached to calcareous building surfaces such as
concrete limestone and plaster, and should never be used in soil.
E.5.6.2.2.1
Metals in soil and air
Corrosion of metal will occur at a rate depending on the type of metal and the nature of its
environment. Environmental factors such as moisture, dissolved salts (thus forming an
electrolyte), degree of aeration, temperature and extent of movement of electrolyte combine
to make this condition a very complex one.
In addition, local conditions, with different natural or industrial contaminants, can cause
significant variations to be observed in different parts of the world. To resolve particular
corrosion problems, consultation with corrosion specialists is strongly recommended.
The effect of contact between dissimilar metals, in association with a surrounding, or partially
surrounding, electrolyte, will lead to increased corrosion of the more anodic metal, and to
decreased corrosion of the more cathodic metal.
The corrosion of the more cathodic metal will not necessarily be fully prevented. The
electrolyte for this reaction may be groundwater, soil with some moisture content or even
moisture condensate in above-ground structures where it is retained by crevices.
Extended earthing systems may suffer from different ground conditions in different parts. This
can enhance the corrosion problems and requires special attention.
In order to minimize corrosion in an LPS:
–
avoid the use of unsuitable metals in an aggressive environment;
–
avoid contact of dissimilar metals, of substantially differing electrochemical or galvanic
activity;
–
use an adequate cross-section of conductors, bonding straps and conducting terminals
and clamps to ensure sufficient corrosion life for the conditions of service;
62305-3 © IEC:2006
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–
provide appropriate filling or insulating material in conductor joints which have not beenwelded conductor joints, so as to exclude moisture;
–
provide sleeve, coat or isolate metals sensitive to corrosive fumes or fluids to the location
of the installation as appropriate;
–
consider the galvanic effects of other metallic items to which the earth electrode is to be
bonded;
–
avoid designs where natural corrosion products from a cathodic metal (e.g. copper) could
impinge on and plate out (the LPS), such as metallic copper on an anodic metal (e.g. steel
or aluminum).
To conform to the foregoing, the following precautions are cited as specific examples:
–
the minimum thickness or diameter of a strand should be 1,5 mm for steel, aluminium,
copper, cuprous alloy or nickel/chrome/steel alloys;
–
an insulating spacer is recommended where contact between closely spaced (or touching)
dissimilar metals could cause corrosion, but such contact is not electrically necessary;
–
steel conductors not otherwise protected should be hot-dipped galvanized to 50 µm
thickness;
–
aluminium conductors should not be buried directly in the ground nor set in or attached
directly to concrete, unless they are completely sleeved with a durable, close-fitting
insulating sleeve;
–
copper/aluminium joints should be avoided wherever possible. In cases where they cannot
be avoided, the connections should be welded or made employing an intermediate layer of
AlCu sheet;
–
fasteners or sleeves for aluminium conductors should be of similar metal and of adequate
cross-section to avoid failure by adverse weather conditions;
–
copper is suitable for use in most earth electrode applications, except for acid, oxygenated
ammoniacal or sulphurous conditions. However, it should be remembered that it will cause
galvanic damage to ferrous materials to which it is bonded. This may require specialist
corrosion advice, particularly when a cathodic protection scheme is used;
–
for roof conductors and down-conductors exposed to aggressive flue gases, particular
attention should be paid to corrosion e.g. through the use of high-alloy steels (>16,5 % Cr,
>2 % Mo, 0,2 % Ti, 0,12 % to 0,22 % N);
–
stainless steel or other nickel alloys may be used for the same corrosion resistance
requirements. However, in anaerobic conditions, such as clay, they will corrode almost as
quickly as mild steel;
–
joints between steel and copper or copper alloys in air, if not welded, should be either fully
tin plated or fully coated with a durable moisture-resistant coating;
–
copper and copper alloys are subject to stress corrosion cracking in ammoniacal fumes
and these materials should not be used for fastenings in these specific applications;
–
in marine/coastal areas, all conductor joints should be welded or effectively fully sealed.
Stainless steel or copper earthing systems can be connected directly to the reinforcement in
concrete.
Galvanized steel earth electrodes in soil should be connected to the steel reinforcement in
concrete by insulating spark gaps capable of conducting a substantial part of the lightning
current (see Tables 8 and 9 for the dimension of connecting conductors). A direct connection
in the soil would significantly increase the risk of corrosion. Insulating spark gaps used should
conform to 6.2 .
NOTE Spark gaps with a protection level U p of 2,5 kV and a minimum I imp of 50 kA (10/350 µ s) are usually
suitable.
Galvanized steel should be used for earth electrodes in soil only when no steel parts
incorporated in the concrete are directly connected to the earth electrode in soil.
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If metal pipes are put in soil and are connected to the equipotential bonding system and to the
earth-termination system, the material of the pipes, where these are not insulated, and the
material of the conductors of the earth system should be identical. Pipes with a protective
covering of paint or asphalt are treated as if they are not insulated. When use of the same
material is not possible, the pipework system should be isolated from the plant sections
connected to the equipotential bonding system by means of insulated sections. The insulated
sections should be bridged by means of spark gaps. Bridging by spark gaps should also be
performed where insulated pieces are installed for cathodic protection of pipework.
Conductors with lead sheaths should not be directly installed in concrete. Conductors with
lead sheaths should be protected against corrosion by provision of either anti-corrosion
bindings or by means of shrunk-on sleeving. Conductors may be protected by a PVC
covering.
Steel earth-termination conductors coming from concrete or from soil at the entry point to the
air should be protected against corrosion for a length of 0,3 m by means of anti-corrosion
wrappings or shrunk-on sleeving. For copper or stainless steel conductors this is not
necessary.
The materials used for the joints between conductors in the soil should have identical
corrosion behaviour to that of the earth-termination conductors. Connection by clamping is not
generally permissible except in cases where such connections are provided with effective
corrosion protection after making the joint. Good experience has been gained with crimped
joints.
Welded joints shall be protected against corrosion.
Practical experience shows that:
–
aluminium should never be used as an earth electrode;
–
lead-sheathed steel conductors are not suitable for use as earth conductors;
–
lead-sheathed copper conductors should not be used in concrete nor in soil with a high
calcium content.
E.5.6.2.2.2
Metals in concrete
The embedding of steel or galvanized steel in concrete causes a stabilization of the natural
potential of the metal, due to the uniformly alkaline environment. In addition, the concrete is of
uniformly, relatively high resistivity – of the order of 200 Ωm or higher.
Consequently, the reinforcing bars in concrete are considerably more resistant to corrosion
than when they are exposed, even if connected externally to more cathodic-electrode
materials.
The use of reinforcing steel as down-conductors does not pose any significant corrosion
problems provided the access points for air-terminations are well encapsulated, e.g. by epoxy
resin putty of adequate thickness.
Galvanized steel strips as foundation earth electrodes may be installed in concrete and
directly connected to the steel reinforcing rods. Copper and stainless steel in concrete are
also accepted and may be connected to the reinforcement steel directly.
Due to the natural potential of steel in concrete, additional earth electrodes outside the
concrete should be made of copper or stainless steel.
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In steel fibre reinforced concrete, the use of steel earth electrodes is not permitted because
during the building process the steel electrode can be pressed down, for instance by the
machines used, and touch the soil. In such a case, the steel faces a serious corrosion risk.
Copper and stainless steel are suitable materials for earth electrodes in steel fibre concrete.
E.6
Internal lightning protection system
E.6.1
General
The requirements for the design of the internal lightning protection system are given in
Clause 6.
The external lightning protection system and its relationship to conductive parts and
installations inside the structure will determine, to a large extent, the need for an internal
lightning protection system.
Consultation with all authorities and parties concerned with equipotential bonding is essential.
The LPS designer and LPS installer should draw attention to the fact that the measures given
in Clause E.6 are very important in order to achieve adequate lightning protection. The
purchaser should be notified accordingly.
The internal lightning protection is the same for all protection levels except for the separation
distances.
The measures necessary for internal lightning protection exceed the equipotentialization
measures for AC power systems in many cases because of the high current rate and current
rise time occurring in the case of a lightning strike.
NOTE
If protection against LEMP is to be considered, IEC 62305-4 should be taken into account.
E.6.1.1
Separation distance
An adequate separation distance, determined according to 6.3, should be maintained between
the external LPS and all conductive parts connected to the equipotential bonding of the
structure.
The separation distance may be evaluated by by Equation (4) shown in 6.3.
The reference length l for the calculation of the separation distance s (see 6.3), should be the
distance between the connection point to the equipotential bonding and the point of proximity
along the down-conductor. The roof and down-conductors should follow a route as straight as
possible to keep the necessary separation distance low.
The length and the path of the conductor within the building running from bonding bar to point
of proximity is generally of little influence on the separation distance, but when this conductor
runs close to a lightning current-carrying conductor the necessary separation distance will be
lower. Figure E.43 and Figure E.44 illustrate how the critical length l used for calculation of
the separation distance s, according to 6.3, is measured on an LPS.
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d
d
1
1
l
l
2
2
IEC 2180/05
Figure E.43a – Calculated separation
distance s < d
IEC 2181/05
Figure E.43b – Calculated separation
distance s > d
Key
1
Metal pipe
2
Equipotential bonding
d
Distance between a down-conductor and a metallic installation inside the building
Length for the evaluation of separation distance s
l
s
Separation distance according to 6.3
NOTE When the distance between a down-conductor and the internal installations cannot be increased above the
calculated separation distance, bonding should be provided at the most distant point, see Figure E.43b.
Figure E.43 – Examples of separation distance between the LPS and metal installations
62305-3 © IEC:2006
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7
d
1
2
1
l
1
4
3
5
5
6
IEC 2182/05
Key
1
Metallic radiator/heater
2
Wall of brickwork or wood
3
Heater
4
Equipotential bonding bar
5
Earth-termination system
6
Connection to the earth-termination system or to the down-conductor
7
Worst case
d
Actual distance
l
Length for evaluation of separation distance s
NOTE
The structure consists of insulating bricks.
Figure E.44 – Directions for calculations of the separation distance s for a worst case
lightning interception point at a distance l from the reference point according to 6.3
In structures where the building components are used as natural down-conductors, for
example steel reinforcement in concrete, the reference point should be the connection point to
the natural down-conductor.
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Structures with outer surfaces that do not contain conductive elements, such as structures of
wood or brickwork, should use the overall distance along the lightning protection conductors l
from the most unfavourable lightning strike point to the point where the equipotential bonding
system of the internal installation is connected to the down-conductor and the earthtermination system, for calculation of the separation distance s , according to 6.3.
When it is not possible to maintain the distance greater than the separation distance s along
the whole length of the considered installation, bonding of the installation to the LPS should
also be performed at the furthest point from the reference bonding point (see Figure E.43b).
Therefore, the electrical conductors should either be re-routed in accordance with the
requirements of the separation distance (see 6.3) or they should be enclosed in a conductive
shield bonded to the LPS at the furthest point from the reference bonding point.
When bonding of installations to the LPS is performed at the reference point and the furthest
point, the separation distance is fulfilled along the whole path of the installation.
The following points are often critical and require particular consideration.
–
In the case of larger structures, the separation distance between the LPS conductors and
the metal installations is often so large that it cannot be implemented. This involves
additional bonding of the LPS to these metal installations. Consequently, a portion of the
lightning current flows via these metal installations to the earth-termination system of the
structure.
–
Electromagnetic interference occurring as a result of these partial currents should be
taken into account when planning the structure installations and designing the lightning
protection electromagnetic zones inside the structure according to IEC 62305-4.
However, the interference will be significantly lower than that caused by an electrical spark at
this point.
In the case of roofs, the distance between the LPS and the electrical installations is often
found to be shorter than the separation distance s given in 6.3. If this is the case, an attempt
should be made to install the LPS or the electrical conductor at a different location.
An agreement should be reached with the person responsible for the electrical installation to
perform a re-routing of electrical circuits which do not conform to the separation distance to
the air-termination conductors on structures.
When the electrical installation cannot be re-routed, bonding to the external LPS should be
carried out in accordance with 6.3.
In some buildings it is not possible to maintain the separation distances as required. Internal
constructions can prevent the designer or installer from assessing situations and making
connections to certain metal parts and electrical conductors. This should be communicated to
the owner of the building.
E.6.2
E.6.2.1
Lightning equipotential bonding (EB)
Design
In the case of an isolated external LPS, the equipotential bonding is established only at
ground level.
In the case of industrial structures, electrically-continuous conductive parts of the structure
and the roof may be generally used as natural LPS components and may be used in the
performance of equipotential bonding.
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It is not only the conductive parts of the structure, and the equipment installed therein, that
should be connected to the equipotential bonding but also the conductors of the power supply
system and the communication equipment. For earth electrodes inside the structure, special
care should be taken to control step voltages. Adequate measures include connecting
concrete reinforcement steel to the earth electrodes locally or providing an equipotentialization mesh in the cellar or basement.
For buildings higher than 30 m, it is recommended to repeat the equipotential bonding at a
level of 20 m and every 20 m above that. However, in all circumstances the separation
distance should be maintained.
This means that, at the very least, on those levels the external down-conductors, the internal
down-conductors and metal parts should be bonded. Live conductors should be bonded via
SPDs.
E.6.2.1.1
Bonding conductors
Bonding conductors should be able to withstand the part of the lightning current flowing
through them.
Conductors bonding metal installations internal to the structure normally do not carry a
significant part of the lightning current. Their minimum dimensions are given in Table 9.
Conductors bonding external conductive parts to the LPS usually carry a substantial part of
the lightning current.
E.6.2.1.2
Surge protective devices
Surge protective devices (SPDs) should withstand the prospective part of the lightning current
flowing through them without being damaged. An SPD should also have the ability to
extinguish electrical power follow-on currents from the power supply if they are connected to
the electrical power conductors.
The selection of SPD shall be performed according to 6.2. Where protection of internal
systems against LEMP is required, SPDs shall also conform to IEC 62305-4.
E.6.2.2
Equipotential bonding of internal conductive parts
Bonding should be provided and installed in such a way that the internal conductive parts, the
external conductive parts and the electrical power and communication systems (for example
computers and security systems) can be bonded by short bonding conductors, and where
necessary utilizing SPDs.
NOTE
Bonding should conform to (pr)EN 60364.
Metal installations, i.e. water, gas, heating and air pipes, lift shafts, crane supports etc. shall
be bonded together and to the LPS at ground level.
Sparking can occur in metal parts not belonging to the structure if those parts are close to the
down-conductors of the LPS. Where this is considered dangerous, adequate bonding
measures according to 6.2 should be used to prevent sparking.
A bonding bar arrangement is shown in Figure E.45.
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8
1
7
9
2
3
11
M
10
4
5
6
M
IEC 2183/05
Key
1
2
3
4
5
6
7
8
9
10
11
M
Power to user
Power meter
House connection box
Power from utility
Gas
Water
Central heating system
Electronic appliances
Screen of antenna cable
Equipotential bonding bar
SPD
Meter
Figure E.45 – Example of an equipotential bonding arrangement
The bonding bars should be located so that they are connected to the earth-termination
system or to the horizontal ring conductors with short conductors.
The bonding bar is preferably installed at the inner side of an outer wall near ground level,
close to the main low-voltage power distribution box and closely connected to the earthtermination system comprising the ring earth electrode, the foundation earth electrode and the
natural earth electrode such as the interconnected reinforcing steel, where applicable.
In extended buildings, several bonding bars may be used provided that they are
interconnected. Very long connections can form big loops leading to large induced currents
and voltages. To minimize these effects, a meshed interconnection of those connections, the
structure and the earthing system according to IEC 62305-4 should be considered.
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In reinforced concrete structures conforming to 4.3, the reinforcement may be used for
equipotential bonding. In this case, an additional meshed network of welded or bolted terminal
joints, described in E.4.3, should be installed in the walls, to which the bonding bars should
be connected via welded conductors.
The minimum cross-sections for a bonding conductor or a bonding connector are given in
Tables 8 and 9. All internal conductive parts of significant size, such as elevator rails, cranes,
metal floors, pipes and electrical services, should be bonded to the nearest bonding bar by a
short bonding conductor at ground level and at other levels if the separation distance
according to 6.3 cannot be maintained. Bonding bars and other bonding parts should
withstand the prospective lightning currents.
In structures with reinforced walls only a minor fraction of the total lightning current is
expected to flow through the bonding parts.
Figures E.46, E.47 and E.48 illustrate bonding arrangements in structures with multiple-point
entries of external services.
2
3
8
1
5
9
4
7
6
IEC 2184/05
Key
1 External conductive part, e.g. metallic water pipe
2
Electric power or communication line
3
Steel reinforcement of the outer concrete wall and the foundation
4
Ring earthing electrode
5
To an additional earthing electrode
6
Special bonding joint
7
Steel reinforced concrete wall, see Key 3
8
SPD
9
Bonding bar
NOTE
The steel reinforcement in the foundation is used as a natural earth electrode.
Figure E.46 – Example of bonding arrangement in a structure with multiple point entries
of external conductive parts using a ring electrode for interconnection of bonding bars
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2
3
4
1
5
10
8
7
9
6
IEC 2185/05
Key
1
Steel reinforcement of the outer concrete wall and foundation
2
Other earthing electrode
3
Bonding joint
4
Internal ring conductor
5
To external conductive, e.g. water pipe
6
Ring earthing electrode, type B earthing arrangement
7
SPD
8
Bonding bar
9
Electric power or communication line
10
To additional earthing electrode, type A earthing arrangement
Figure E.47 – Example of bonding in the case of multiple point entries of external
conductive parts and an electric power or communication line using an internal ring
conductor for interconnection of the bonding bars
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1
2
3
6
8
7
4
3
5
IEC 2186/05
Key
1 Electric power or communication line
2 External horizontal ring conductor (above ground)
3 External conductive part
4 Down-conductor joint
5 Steel reinforcement in the wall
6 Bonding joint to construction steel
7 Bonding bar
8 SPD
Figure E.48 – Example of bonding arrangement in a structure with multiple point entries
of external conductive parts entering the structure above ground level
E.6.2.3
Lightning equipotential bonding for external conductive parts
No additional information available.
E.6.2.4
Lightning equipotential bonding for electrical and electronic systems within
the structure to be protected
Details for lightning equipotential bonding for internal systems are given in IEC 62305-4.
E.6.2.5
Equipotential bonding of external services
Preferably, the external conductive parts and the electrical power and communication lines
should enter the structure near ground level at a common location.
Equipotential bonding should be performed as close as possible to the entry point into the
building. In the case of a low voltage power supply, this is immediately downstream of the
service entrance box (subject to approval of the local power company).
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The bonding bar at this common location of entry should be connected with short bonding
conductors to the earth-termination system.
If the services entering the building are shielded lines, the shields shall be connected to the
bonding bar. The overvoltage reaching the active conductors is a function of the size of the
partial lightning current over the screen (i.e. according to Annex B) and the cross-section of
the shield. Annex E of IEC 62305-1 provides a method to estimate this current. SPDs are
necessary if the expected overvoltages exceed the specification of the line and connected
objects.
If the services entering the building are not shielded, the partial lightning current will flow on
the active conductors. In this case, SPDs with lightning current capabilities should be placed
at the entry point. PE or PEN conductors may be connected to the bonding bar directly.
When the external conductive parts, the electrical power and communication lines have to
enter the structure at different locations, and therefore need several bonding bars to be
installed, the bonding bars should be connected as closely as possible to the earthtermination system, i.e. the ring earth electrode, to the reinforcement of the structure and to
the foundation earth electrode of the structure, if applicable.
When a type A earthing arrangement is utilized as a part of the LPS, the bonding bars should
be connected to individual earth electrodes and, in addition, they should be interconnected by
an internal ring conductor or an internal conductor forming a partial ring.
For entries of external services above the earth surface, the bonding bars should be
connected to a horizontal ring conductor inside or outside the outer wall bonded to the downconductors of the LPS and to the metallic reinforcement of the structure, if applicable.
The ring conductor should be connected to the steel reinforcement, and other metallic
elements of the structure, at regular subdivisions of the distance between the downconductors as stated in Table 4.
In buildings principally designed for computer centres, communication buildings and other
structures requiring a low level of LEMP induction effects, the ring conductor should be
connected to the reinforcement typically every 5 m.
For the bonding of external services in reinforced concrete buildings which contain large
communication or computer installations, and for structures where EMC demands are severe,
a ground plane with multiple connections to the metallic reinforcement of the structure or
other metallic elements should be used.
E.6.3
Electrical insulation of the external LPS
An adequate separation according to 6.3 is to be maintained between the external LPS and all
conductive parts connected to the equipotential bonding of the structure.
For details see E.6.1.1. For low structures some examples and calculations of k c in 6.3 are
given in Figure E.2.
E.6.4
Protection against effects of induced currents in internal systems
Currents in the conductors of the external LPS may induce excessive over-voltages in the
conductor loops of the internal installations by the effect of magnetic coupling. Overvoltages
may cause failures of internal systems.
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Since practically all buildings contain electronic equipment, the effect of the electromagnetic
field of the external and internal down-conductors should be taken into account in the
planning of the lightning protection system.
Protection measures against overvoltages are given in IEC 62305-4.
E.7
Maintenance and inspection of the LPS
E.7.1
Scope of inspections
Inspection of the LPS should be conducted by a lightning protection specialist in accordance
with the recommendations of Clause E.7.
The inspector should be provided with the LPS design report containing the necessary
documentation of the LPS such as design criteria, design description and technical drawings.
The LPS inspector should also be provided with previous LPS maintenance and inspection
reports.
All LPS should be inspected on the following occasions:
–
during installation of the LPS, especially during installation of components which are
concealed in the structure and will become inaccessible;
–
after the completion of the LPS installation;
–
on a regular basis according to Table E.2.
Table E.2 – Maximum period between inspections of an LPS
Visual inspection
Complete inspection
(year)
(year)
Critical systems
complete inspection
(year)
I and II
1
2
1
III and IV
2
4
1
Protection level
NOTE Lightning protection systems utilized in applications involving structures with a risk of explosion should be
visually inspected every 6 months. Electrical testing of the installation should be performed once a year.
An acceptable exception to the yearly test schedule would be to perform the tests on a 14 to 15 month cycle where
it is considered beneficial to conduct earth resistance testing over different times of the year to get an indication of
seasonal variations.
The inspection frequencies given in Table E.2 should apply where no specific requirements
are identified by the authority having jurisdiction.
NOTE If national authorities or institutions require regular tests of the electrical system of a structure, it is
recommended to test the lightning protection system with regard to the functioning of the Internal lightning
protection measures including the lightning protection equipotential bonding with electric systems at the same time.
Older installations analogously should be related to a lightning protection class or the test intervals should be
taken from the local or any other test specifications such as construction guide lines, technical regulations,
instructions, industrial safety and protection of labour laws.
The LPS should be visually inspected at least annually. In some areas where severe weather
changes and extreme weather conditions occur, it is advisable to visually inspect the system
more often than indicated in Table E.2. Where the LPS forms part of the client’s planned
maintenance programme, or is a requirement of the building insurers, the LPS may be
required to be fully tested annually.
The interval between the LPS inspections should be determined by the following factors:
–
classification of structure protected, especially with regard to the consequential effects of
damage;
–
class of LPS;
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–
local environment, for example a corrosive atmosphere environment should have short
intervals between inspections;
–
the materials of the individual LPS components;
–
the type of surface to which the LPS components are attached;
–
the soil condition and associated corrosion rates.
In addition to the above, an LPS should be inspected whenever any significant alteration or
repairs are made to a protected structure and also following any known lightning discharge to
the LPS.
A total inspection and test should be completed every two to four years. Systems in critical
environmental conditions, for example parts of the LPS exposed to severe mechanical
stresses such as flexible bonding straps in high wind areas, SPDs on pipelines, outdoor
bonding of cables etc., should have a complete inspection every year.
In most geographical areas, and especially in areas which experience extreme seasonal
changes in temperature and rainfall, the variation of the earthing resistance should be taken
into account by measuring the resistivity depth profile in different weather periods.
An improvement of the earthing system should be considered when the measured resistance
values show larger changes in the resistance than anticipated in the design; especially when
the resistance increases steadily between inspections.
E.7.2
E.7.2.1
Order of inspections
Inspection procedure
The purpose of this inspection is to ensure that the LPS conforms to this standard in all
respects.
The inspection includes checking technical documentation, visual inspections, testing and
logging in an inspection report.
E.7.2.2
Checking of technical documentation
Technical documentation should be checked for completeness, conformity to this standard
and agreement with the plant as executed.
E.7.2.3
Visual inspections
Visual inspections should be made to ascertain that
–
the design conforms to this standard,
–
the LPS is in good condition,
–
there are no loose connections and no accidental breaks in the LPS conductors and joints,
–
no part of the system has been weakened by corrosion, especially at ground level,
–
all visible earth connections are intact (functionally operational),
–
all visible conductors and system components are fastened to the mounting surfaces and
components which provide mechanical protection are intact (functionally operational) and
in the right place,
–
there have not been any additions or alterations to the protected structure which would
require additional protection,
–
there has been no indication of damage to the LPS, to SPDs or any failures of fuses which
protect SPDs,
–
correct equipotential bonding has been established for any new services or additions
which have been made to the interior of the structure since the last inspection, and that
continuity tests have been performed for these new additions,
62305-3 © IEC:2006
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–
bonding conductors and connections inside the structure are present and intact
(functionally operational),
–
separation distances are maintained,
–
bonding conductors, joints, shielding devices, cable routing and SPDs have been checked
and tested.
E.7.2.4
Testing
Inspection and testing of the LPS includes visual inspections and should be completed by the
following actions:
–
performing continuity tests, especially continuity of those parts of the LPS which were not
visible for inspection during the initial installation and are not subsequently available for
visual inspection;
–
conducting earth resistance tests of the earth-termination system. The following isolated
and combined earth measurements and checks should be made and the results recorded
in an LPS inspection report.
NOTE High frequency measurement is possible at the installation stage as well as for the maintenance of the
earthing system to check adequacy between the designed earthing system and the need.
a) The resistance to earth of each local earth electrode and where reasonably practical the
resistance to earth of the complete earth-termination system.
Each local earth electrode should be measured in isolation with the test point between the
down-conductor and earth electrode in the disconnected position (isolated measurement).
If the resistance to earth of the earth-termination system as a whole exceeds 10 Ω, a
check should be made to ascertain that the electrode conforms to Figure 2.
If there is a significant increase in the value of the earth resistance, additional
investigations should be made to determine the reason for the increase and measures
taken to improve the situation.
For earth electrodes in rocky soil, the requirements of E.5.4.3.5 should be followed. The
10 Ω requirement is not applicable in this case.
b) The results of a visual check of all conductors, bonds and joints or their measured
electrical continuity.
If the earth-termination system does not conform to these requirements, or checking the
requirements is not possible because of a lack of information, the earth-termination system
should be improved by installing extra earth electrodes or installing a new earth-termination
system.
E.7.2.5
Documentation of inspection
LPS inspection guides should be prepared to facilitate LPS inspections. They should contain
sufficient information to guide the inspector through the inspection process so that all areas of
importance are documented such as the method of LPS installation, the type and condition of
the LPS components, test methods and the proper recording of the test data obtained.
The inspector should compile an LPS inspection report, which should be kept together with
the LPS design report and the previously compiled LPS maintenance and inspection reports.
The LPS inspection report should contain the following information:
–
general conditions of air-termination conductors, and other air-termination components;
–
general level of corrosion and the condition of the corrosion protection;
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–
security of attachment of the LPS conductors and components;
–
earth resistance measurements of the earth-termination system;
–
any deviation from the requirements of this standard;
–
documentation of all changes and extension of the LPS and any changes to the structure.
In addition, the LPS construction drawings and the LPS design description should be
reviewed;
–
the results of the tests performed.
E.7.3
Maintenance
The LPS should be maintained regularly to ensure that it does not deteriorate but continues to
fulfil the requirements to which it was originally designed. The design of an LPS should
determine the necessary maintenance and inspection cycle according to Table E.2.
The LPS maintenance programme should ensure a continuous updating of the LPS to the
current issue of this standard.
E.7.3.1
General remarks
LPS components tend to lose their effectiveness over the years because of corrosion,
weather-related damage, mechanical damage and damage from lightning strokes.
The inspection and maintenance programmes should be specified by an authority, the LPS
designer or the LPS installer, in conjunction with the owner of the structure or an appointed
representative.
To carry out maintenance work and to perform inspections of an LPS the two programmes,
inspection and maintenance, should be coordinated.
Maintenance of an LPS is important even though the LPS designer has taken special
precautions to provide corrosion protection and has dimensioned the LPS components
according to their particular exposure to lightning damage and weather elements in addition to
the requirements of this standard.
The mechanical and electrical characteristics of the LPS should be fully maintained
throughout the entire lifetime of the LPS in order to conform to the design requirements of this
standard.
It may be necessary to modify the LPS if modifications are carried out on the building or its
equipment or if the purpose for which the building is utilized is altered.
If an inspection shows that repairs are necessary, those repairs should be executed without
delay and not be postponed until the next maintenance cycle.
E.7.3.2
Maintenance procedure
Periodic maintenance programmes should be established for all LPS.
The frequency of maintenance procedures is dependent on the following:
–
weather- and environment-related degradation;
–
exposure to actual lightning damage;
–
protection level assigned to the structure.
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LPS maintenance procedures should be established for each particular LPS and should
become a part of the overall maintenance programme for the structure.
A maintenance programme should contain a list of routine items to serve as a checklist so
that definite maintenance procedures are followed regularly in order to make it possible to
compare recent results with previous ones.
A maintenance programme should contain provisions for the following:
–
verification of all LPS conductors and system components;
–
verification of the electrical continuity of the LPS installation;
–
measurement of the resistance to earth of the earth termination system;
–
verification of SPDs;
–
re-fastening of components and conductors;
–
verification to ensure the effectiveness of the LPS has not been reduced after additions to,
or changes in, the structure and its installations.
E.7.3.3
Maintenance documentation
Complete records should be kept of all maintenance procedures and should include corrective
actions taken or required.
Maintenance procedure records should provide a means of evaluating LPS components and
the LPS installation.
The LPS maintenance record should serve as a basis for reviewing maintenance procedures
as well as for updating maintenance programmes. The LPS maintenance records should be
kept together with the LPS design and the LPS inspection reports.
62305-3 © IEC:2006
– 307 –
Bibliography
IEC 60050(426):1990, International Electrotechnical Vocabulary (IEV) – Chapter 426:
Electrical apparatus for explosive atmospheres
IEC 61000-5-2, Electromagnetic compatibility (EMC) – Part 5: Installation and mitigation
guidelines – Section 2: Earthing and cabling
IEC 61643-1:2005, Low-voltage surge protective devices – Part 1: Surge protective devices
connected to low-voltage power distribution systems – Requirements and tests
EN 50164 (all parts), Lightning Protection Components (LPC)
EN 50164-1:1999, Lightning Protection Components (LPC) – Part 1: Requirements for
connection components
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